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physics
mechanics
Questions and Answers of
Mechanics
Most projectiles continually move farther from the origin during their flight, but this is not the case if the launch angle is greater than cos-1 (1/3) = 70.5°. For example, the projectile shown
If pellets shot at the same angle are compared, which of the following is true? A. A lighter pellet travels farther because of its higher ejection speed. B. A heavier pellet travels farther because
What is the maximum height above its launch site of a 20-mg pellet that's launched at an angle of 20° above the horizontal? A. 5.1 cm B. 4.5 cm C. 1.2 cm D. 6.0 mm
Two canoeists start paddling at the same time and head toward a small island in a lake, as shown in FIGURE 4-18. Canoeist 1 paddles with a speed of 1.10 m/s at an angle of 45° north of east.
A pellet launched at 30° above the horizontal that spends 0.15 s in the air before returning to its original level has approximately what mass?A. 2 mgB. 9 mgC. 14 mgD. 20 mg
What is the maximum range of a 5-mg pellet that lands at the same height from which it is ejected? A. 14 cm B. 20 cm C. 40 cm D. 78 cm
(a) At what launch angle greater than 54.0° does the golf ball just barely miss the top of the tree in front of the green? Assume that the ball has an initial speed of 13.5 m/s, and that the tree is
Suppose that the golf ball is launched with a speed of 15.0 m/s at an angle of 57.5° above the horizontal, and that it lands on a green 3.50 m above the level where it was struck.(a) What horizontal
Suppose the ball is dropped at the horizontal distance of 5.50 m, but from a new height of 5.00 m. The dolphin jumps with the same speed of 12.0 m/s.(a) What launch angle must the dolphin have if it
Suppose we change the dolphin's launch angle to 45.0°, but everything else remains the same. Thus, the horizontal distance to the ball is 5.50 m, the drop height is 4.10 m, and the dolphin's launch
A whole brick has more mass than half a brick, thus the whole brick is harder to accelerate. Why doesn't a whole brick fall more slowly than half a brick? Explain.
A bird cage, with a parrot inside, hangs from a scale. The parrot decides to hop to a higher perch. What can you say about the reading on the scale (a) When the parrot jumps, (b) When the parrot is
A friend tells you that since his car is at rest, there are no forces acting on it. How would you reply?
To clean a rug, you can hang it from a clothesline and beat it with a tennis racket. Use Newton's laws to explain why beating the rug should have a cleansing effect.
You've probably seen pictures of someone pulling a tablecloth out from under glasses, plates, and silverware set out for a formal dinner. Perhaps you've even tried it yourself. Using Newton's laws of
Is it possible for an object to be moving in one direction while the net force acting on it is in another direction? If your answer is yes, provide an example. If your answer is no, explain why not.
In the movie The Rocketeer, a teenager discovers a jet-powered backpack in an old barn. The backpack allows him to fly at incredible speeds. In one scene, however, he uses the backpack to rapidly
When a dog gets wet, it shakes its body from head to tail to shed the water. Explain, in terms of Newton's first law, why this works.
A block of mass m hangs from a string attached to a ceiling, as shown in FIGURE 5-24. An identical string hangs down from the bottom of the block. Which string breaks if(a) The lower string is pulled
Two untethered astronauts on a space walk decide to take a break and play catch with a baseball. Describe what happens as the game of catch progresses.
An object of mass m is initially at rest. After a force of magnitude F acts on it for a time T, the object has a speed v. Suppose the mass of the object is doubled, and the magnitude of the force
In baseball, a pitcher can accelerate a 0.15- kg ball from rest to 98 mi/h in a distance of 1.7 m. (a) What is the average force exerted on the ball during the pitch? (b) If the mass of the ball is
A major-league catcher gloves a 92 mi/h pitch and brings it to rest in 0.15 m. If the force exerted by the catcher is 803 N, what is the mass of the ball?
Driving home from school one day, you spot a ball rolling out into the street (FIGURE 5-27). You brake for 1.20 s, slowing your 950-kg car from 16.0 m/s to 9.50 m/s.(a) What was the average force
A 747 jetliner lands and begins to slow to a stop as it moves along the runway. If its mass is 3.50 × 105 kg, its speed is 75.0 m/s, and the net braking force is 7.25 × 105 N,(a) What is its speed
The vx-versus-time graph for a 1.8-kg object is shown in FIGURE 5-28. A single force acts on the object, and the force has only an x component. What is Fx at(a) t = 0.50 s,(b) t = 2.0 s,(c) t = 4.0 s?
A drag racer crosses the finish line doing 202 mi/h and promptly deploys her drag chute (the small parachute used for braking). (a) What force must the drag chute exert on the 891-kg car to slow it
A small car collides with a large truck. (a) Is the magnitude of the force experienced by the car greater than, less than, or equal to the magnitude of the force experienced by the truck? (b) Choose
A small car collides with a large truck. (a) Is the acceleration experienced by the car greater than, less than, or equal to the acceleration experienced by the truck? (b) Choose the best explanation
As you catch a 0.14-kg ball it accelerates at − 320 m/s2 and comes to rest in your hand. What force does the ball exert on your hand?
A woodpecker exerts a 230-N force on a tree trunk during its effort to find hidden insects to eat. If its head has an effective mass of 0.025 kg, what is the acceleration of its head away from the
On a planet far, far away, an astronaut picks up a rock. The rock has a mass of 5.00 kg, and on this particular planet its weight is 40.0 N. If the astronaut exerts an upward force of 46.2 N on the
On vacation, your 1400-kg car pulls a 560-kg trailer away from a stoplight with an acceleration of 1.85 m/s2.(a) What is the net force exerted on the trailer?(b) What force does the trailer exert on
An 85-kg parent and a 24-kg child meet at the center of an ice rink. They place their hands together and push.(a) Is the force experienced by the child greater than, less than, or the same as the
A force of magnitude 7.50 N pushes three boxes with masses m1 = 1.30 kg, m2 = 3.20 kg, and m3 = 4.90 kg, as shown in FIGURE 5-29. Find the magnitude of the contact force(a) Between boxes 1 and 2,(b)
A force of magnitude 7.50 N pushes three boxes with masses m1 = 1.30 kg, m2 = 3.20 kg, and m3 = 4.90 kg, as shown in FIGURE 5-30. Find the magnitude of the contact force(a) Between boxes 1 and 2,(b)
Two boxes sit side-by-side on a smooth horizontal surface. The lighter box has a mass of 5.2 kg; the heavier box has a mass of 7.4 kg.(a) Find the contact force between these boxes when a horizontal
A skateboarder on a ramp is accelerated by a nonzero net force. For each of the following statements, state whether it is always true, never true, or sometimes true. (a) The skateboarder is moving in
Three objects, A, B, and C, have x and y components of velocity that vary with time as shown in FIGURE 5-31. What is the direction of the net force acting on(a) Object A,(b) Object B, and(c) Object
A farm tractor tows a 3300-kg trailer up a 14° incline with a steady speed of 2.8 m/s. What force does the tractor exert on the trailer? (Ignore friction.)
A shopper pushes a 7.5-kg shopping cart up a 13° incline, as shown in FIGURE 5-32. Find the magnitude of the horizontal force, F(vector), needed to give the cart an acceleration of 1.41 m/s2.
Two crewmen pull a raft through a lock, as shown in FIGURE 5-33. One crewman pulls with a force of 130 N at an angle of 34° relative to the forward direction of the raft. The second crewman, on
In a grocery store, you push a 15.4-kg shopping cart horizontally with a force of 13.4 N. If the cart starts at rest, how far does it move in 2.50 s?
A hockey puck is acted on by one or more forces, as shown in FIGURE 5-34. Rank the four cases, A, B, C, and D, in order of the magnitude of the puck's acceleration, starting with the smallest.
To give a 19-kg child a ride, two teenagers pull on a 3.7-kg sled with ropes, as indicated in FIGURE 5-35. Both teenagers pull with a force of 55 N at an angle of 35° relative to the forward
A 65-kg skier speeds down a trail, as shown in FIGURE 5-36. The surface is smooth and inclined at an angle of 22° with the horizontal.(a) Find the direction and magnitude of the net force acting
An object acted on by three forces moves with constant velocity. One force acting on the object is in the positive x direction and has a magnitude of 6.5 N; a second force has a magnitude of 4.4 N
A train is traveling up a 2.88° incline at a speed of 4.31 m/s when the last car breaks free and begins to coast without friction.(a) How much time does it take for the last car to come to rest
In FIGURE 5-37 we show the Earth, Moon, and Sun (not to scale) in their relative positions at the time when the Moon is in its third-quarter phase. Though few people realize it, the force exerted on
You pull upward on a stuffed suitcase with a force of 105 N, and it accelerates upward at 0.725 m/s2. What are(a) The mass(b) The weight of the suitcase?
A newborn baby's brain grows rapidly. In fact, it has been found to increase in mass by about 1.6 mg per minute. (a) How much does the brain's weight increase in one day? (b) How much time does it
Suppose a rocket launches with an acceleration of 30.5 m/s2. What is the apparent weight of a 92-kg astronaut aboard this rocket?
During an episode of turbulence in an airplane you feel 190 N heavier than usual. If your mass is 78 kg, what are the magnitude and direction of the airplane's acceleration?
You are pulling your little sister on her sled across an icy (frictionless) surface. When you exert a constant horizontal force of 120 N, the sled has an acceleration of 2.5 m/s2. If the sled has a
At the bow of a ship on a stormy sea, a crewman conducts an experiment by standing on a bathroom scale. In calm waters, the scale reads 182 lb. During the storm, the crewman finds a maximum reading
As part of a physics experiment, you stand on a bathroom scale in an elevator. Though your normal weight is 610 N, the scale at the moment reads 730 N.(a) Is the acceleration of the elevator upward,
When you weigh yourself on good old terra firma (solid ground), your weight is 142 lb. In an elevator your apparent weight is 121 lb. What are the direction and magnitude of the elevator's
A 1.21-g samara- the winged fruit of a maple tree-falls toward the ground with a constant speed of 1.1 m/s (FIGURE 5-38).(a) What is the force of air resistance exerted on the samara?(b) If the
When you lift a bowling ball with a force of 82 N, the ball accelerates upward with an acceleration a. If you lift with a force of 92 N, the ball's acceleration is 2a. Find(a) The weight of the
A 23-kg suitcase is pulled with constant speed by a handle at an angle of 25° above the horizontal. If the normal force exerted on the suitcase is 180 N, what is the force F applied to the handle?
(a) Draw a free-body diagram for the skier in Problem 32.(b) Determine the normal force acting on the skier.In Problem 32A 65-kg skier speeds down a trail, as shown in FIGURE 5-36. The surface is
A 9.3-kg child sits in a 3.7-kg high chair.(a) Draw a free-body diagram for the child, and find the normal force exerted by the chair on the child.(b) Draw a free-body diagram for the chair, and find
FIGURE 5-39 shows the normal force N experienced by a rider of weight W = mg on a Ferris wheel as a function of time.(a) At what time, A, B, C, or D, is the rider accelerating upward?(b) What is the
FIGURE 5-40 shows the normal force N as a function of the angle θ for the suitcase shown in Figure 5-20. Determine the magnitude of the force F(vector) for each of the three curves shown in Figure
A 0.53-kg billiard ball initially at rest is given a speed of 12 m/s during a time interval of 4.0 ms. What average force acted on the ball during this time?
A 5.0-kg bag of potatoes sits on the bottom of a stationary shopping cart.(a) Sketch a free-body diagram for the bag of potatoes.(b) Now suppose the cart moves with a constant velocity. How does this
(a) Find the normal force exerted on a 2.9-kg book resting on a surface inclined at 36° above the horizontal. (b) If the angle of the incline is reduced, do you expect the normal force to increase,
A gardener mows a lawn with an old-fashioned push mower. The handle of the mower makes an angle of 32° with the surface of the lawn. (a) If a 68-N force is applied along the handle of the 17-kg
An ant walks slowly away from the top of a bowling ball, as shown in FIGURE 5-41. If the ant starts to slip when the normal force on its feet drops below one-half its weight, at what angle
Riding in an elevator moving upward with constant speed, you begin a game of darts. (a) Do you have to aim your darts higher than, lower than, or the same as when you play darts on solid ground? (b)
Riding in an elevator moving with a constant upward acceleration, you begin a game of darts. (a) Do you have to aim your darts higher than, lower than, or the same as when you play darts on solid
Give the direction of the net force acting on each of the following objects. If the net force is zero, state "zero." (a) A car accelerating northward from a stoplight. (b) A car traveling southward
You jump out of an airplane and open your parachute after an extended period of free fall. (a) To decelerate your fall, must the force exerted on you by the parachute be greater than, less than, or
In a tennis serve, a 0.070-kg ball can be accelerated from rest to 36 m/s over a distance of 0.75 m. Find the magnitude of the average force exerted by the racket on the ball during the serve.
The left ventricle of the human heart expels about 0.070 kg of oxygenated blood straight upward into the ascending aorta with a force of 5.5 N. What is the acceleration of the blood as it enters the
A 92-kg water skier floating in a lake is pulled from rest to a speed of 12 m/s in a distance of 25 m. What is the net force exerted on the skier, assuming his acceleration is constant?
A 51.5-kg swimmer with an initial speed of 1.25 m/s decides to coast until she comes to rest. If she slows with constant acceleration and stops after coasting 2.20 m, what was the force exerted on
The ax-versus-time graph for a 2.0-kg object is shown in FIGURE 5-42. Draw the corresponding Fx-versus-time graph, assuming only a single force acts on the object.
A skateboarder starts from rest and rolls down a ramp that is inclined at an angle of 15° below the horizontal. Friction can be ignored.(a) What is the acceleration of the skateboarder?(b) What is
The rotors of a 15,200-kg heavy-lift helicopter exert a downward force of 322,000 N in order to accelerate itself and its external cargo upward at 0.50 m/s2. By itself, what upward force does the
As it pulls itself up to a branch, a chimpanzee accelerates upward at 2.2 m/s2 at the instant it exerts a 260-N force downward on the branch. The situation is shown in FIGURE 5-43.(a) In what
Each of the three identical hockey pucks shown in FIGURE 5-44 is acted on by a 3-N force. Puck A moves with a speed of 7 m/s in a direction opposite to the force; puck B is instantaneously at rest;
NASA plans to use a new type of rocket, a Variable Specific Impulse Magneto plasma Rocket (VASIMR), on future missions. If a VASIMR can produce 6.0 N of thrust (force), and has a mass of 620 kg,(a)
An object of mass m = 5.95 kg has an acceleration a(vector) = (1.17 m/s2)x̂ + (–0.664 m/s2)ŷ. Three forces act on this object: F(vector)1, F(vector)2, and F(vector)3. Given that F(vector)1 =
At the local grocery store, you push a 14.5-kg shopping cart. You stop for a moment to add a bag of dog food to your cart. With a force of 12.0 N, you now accelerate the cart from rest through a
Biomechanical research has shown that when a 67-kg person is running, the force exerted on each foot as it strikes the ground can be as great as 2300 N.(a) What is the ratio of the force exerted on
A 0.5-kg object is acted on by a force whose x component varies with time as shown in FIGURE 5-26. Draw the corresponding ax-versus-time graph for this object.
To become airborne, a 2.0-g grasshopper requires a takeoff speed of 2.7 m/s. It acquires this speed by extending its hind legs through a distance of 3.7 cm.(a) What is the average acceleration of the
On an aircraft carrier, a jet can be catapulted from 0 to 155 mi/h in 2.00 s. If the average force exerted by the catapult is 9.35 × 105 N, what is the mass of the jet?
A 79-kg person stands on a bathroom scale and rides in an elevator whose vy-versus-time graph is shown in FIGURE 5-45. What is the reading on the scale at(a) t = 1.0 s,(b) t = 4.0 s,(c) t = 8.0 s?
An archer shoots a 0.024-kg arrow at a target with a speed of 54 m/s. When it hits the target, it penetrates to a depth of 0.083 m.(a) What was the average force exerted by the target on the
An apple of mass m = 0.13 kg falls out of a tree from a height h = 3.2 m.(a) What is the magnitude of the force of gravity, mg, acting on the apple?(b) What is the apple's speed, v, just before it
Paleontologists estimate that if a Tyrannosaurus rex had tripped and fallen, the ground would have exerted a normal force of approximately 260,000 N on its torso as it landed. Assuming the torso has
The NASA spacecraft Deep Space 1 was shut down on December 18, 2001, following a three-year journey to the asteroid Braille and the comet Borrelly. This spacecraft used a solar-powered ion engine to
Your groceries are in a bag with paper handles. The two handles together will tear off if a force greater than 51.5 N is applied to them. What is the greatest mass of groceries that can be lifted
The motion of jumping insects is of interest not only to biologists, but also to those who design robots. FIGURE 5-46 shows the speed-versus-time graph for two different takeoff jumps of a 19-mg
At the airport, you observe some of the jets as they take off. With your watch you find that it takes about 35 seconds for a plane to go from rest to takeoff speed. In addition, you estimate that the
You drop two balls of equal diameter from the same height at the same time. Ball 1 is made of metal and has a greater mass than ball 2, which is made of wood. The upward force due to air resistance
Researchers have found that a gecko's foot is covered with hundreds of thousands of small hairs (setae) that allow it to walk up walls and even across ceilings. A single foot pad, which has an area
Two boxes are at rest on a smooth, horizontal surface. The boxes are in contact with one another. If box 1 is pushed with a force of magnitude F = 12.00 N, the contact force between the boxes is 8.50
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