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college physics reasoning

Questions and Answers of College Physics Reasoning

Consider again the airplane in Problem 38, but now suppose the wind is directed in an easterly direction. How long does it take the airplane to travel a distance between two cities that are 300 km
An airplane flies from Boston to San Francisco (a distance of 5000 km) in the morning and then immediately returns to Boston. The airplane’s speed relative to the air is 250 m/s. The wind is
Round trip. An airplane flies from Chicago to New Orleans (a distance of 1500 km) in the morning and then immediately returns to Chicago. The airplane’s speed relative to the air is 250 m/s. The
A 35-m-wide river flows in a straight line (the x direction) with a speed of 0.25 m/s. A boat is rowed such that it travels directly across the river (along y). If the boat takes exactly 4 minutes to
Two children pull a sled of mass 15 kg along a friction less surface as shown in Figure P4.43. (a) Find the magnitude and direction of the sled€™s acceleration. (b) How long does
Consider the crates in Problem 12 (Fig. P4.12). Assume there is no friction between m1and the table. (a) Sketch all the forces on the crates. Include a coordinate system. (b) Determine the
When a car is traveling at 25 m/s on level ground, the stopping distance is found to be 22 m. This distance is measured by pushing hard on the brakes so that the wheels skid on the pavement. The same
A block slides down an inclined plane that makes an angle of 40° with the horizontal. There is friction between the block and the plane. (a) Sketch all the forces on the block. Include a
A sled is pulled with a horizontal force of 20 N along a level trail, and the acceleration is found to be 0.40 m/s2. An extra mass m = 4.5 kg is placed on the sled. If the same force is just barely
Two crates are connected by a mass less rope that passes over a pulley as shown in Figure 4.26. If the crates have mass 35 kg and 85 kg, what is their acceleration? If the system begins at rest, with
A hockey puck is sliding down an inclined plane with angle Î¸ = 15° as shown in Figure P4.49. If the puck is moving with a constant speed, what is the coefficient of kinetic friction
Hang time. LeBron James decides to jump high enough to dunk a basketball. What is the approximate force between the floor and his feet while he is jumping from the floor?
Calculate the terminal speed for a bacterium in water. Use the expression for the drag force in Equation 3.23. Assume the bacterium has a mass m = 4 × 10–15 kg, a drag coefficient C = 0.02 N •
In traction. When a large bone such as the femur is broken, the two pieces are often pulled out of alignment by the complicated combination of tension and compression forces that arise from the
A mass with M = 102 kg is attached to the bottom of a block-and-tackle pulley system as depicted in Figure P3.65. How much tension force is needed to keep the mass at its current position?Figure
What is the approximate speed at which the force of air drag on a car is equal to the weight of the car?
A bullet of mass 10 g leaves the barrel of a rifle at 300 m/s. Assuming the force on the bullet is constant while it is in the barrel, find the magnitude of this force.
When an airplane takes off, it accelerates on the runway starting from rest. What is the magnitude of this runway acceleration for a passenger jet?
Calculate the terminal speed for a pollen grain falling through the air using the drag force Equation 3.20. Assume the pollen grain has a diameter of 1 mm and a density of 0.2 g/cm3. If this grain is
Consider a skydiver who lands on the ground with a speed of 3 m/s. What is the approximate force on the skydiver’s legs when she lands?
Calculate the terminal speed for a baseball. A baseball’s diameter is approximately d = 0.070 m, and its mass is m = 0.14 kg. Express your answer in meters per second and miles per hour.
Hail forms high in the atmosphere and can be accelerated to a high speed before it reaches the ground. Estimate the terminal speed of a spherical hailstone that has a diameter of 2.0 cm.
Calculate the force of air drag on a hockey puck moving at 30 m/s. A hockey puck is approximately 3.0 cm tall and 8.0 cm in diameter.
The following items are dropped from an airplane. Rank them in order from lowest terminal speed to highest and justify your ranking.(a) Bowling ball(b) Beach ball(c) Spear or javelin (pointing
A Styrofoam ball of radius 28 cm falls with a terminal speed of 5.0 m/s. What is the mass of the ball?
You are a secret agent and find that you have been pushed out of an airplane without a parachute. Fortunately, you are wearing a large overcoat (as secret agents often do). Thinking quickly, you are
Calculate the drag force on a bullet that is 5.0 mm in diameter and moving at a speed of 600 m/s. If the mass of the bullet is 10 g, compare this force to the weight of the bullet and to your own
The force exerted on a bacterium by its flagellum is 4 × 10-13 N. Find the velocity of the bacterium in water. Assume a size r = 1 mm.
A textbook rests at the edge of a desk of average height. (a) If the book gently tips off the desk, what is its approximate speed when it hits the floor? (b) If the height of the desk were
The kick experienced when firing a rifle can be explained by Newton’s third law. A .22-caliber rifle has a mass M = 5.2 kg, and a bullet with a mass m = 3.0 g leaves the barrel of the gun at a
What is your reaction time? The following simple method can be employed to determine reaction time. A partner holds a meter stick by pinching it at the top and letting it hang vertically. To measure
Deer in the headlights. There are two important time intervals to consider when coming to an emergency stop while driving. The first is the driver’s reaction time to get a foot on the brake pedal,
A boy pushes a 3.1-kg book against a vertical wall with a horizontal force of 40 N. What is the minimum coefficient of friction that will keep the book in place without sliding?
An impish young lad stands on a bridge 10 m above a lake and drops a water balloon on a boat of unsuspecting tourists. Although the boat is traveling at a speed of 7.5 m/s, the boy manages to land
Two mischievous children drop water balloons from a bridge as depicted in Figure P3.87. Each water balloon is approximately 30 cm in diameter, and in this figure the red balloon is about 1.8 m below
A subway train is designed with a maximum acceleration of +0.20 m/s2, which allows for both passenger safety and comfort. (a) If subway stations are 1.2 km apart, what is the maximum velocity
A spring scale indicates that a helium balloon tied to it produces a tension of 0.20 N in the string. The string is then cut, and the balloon rises until it comes to rest on the ceiling. (a)
Slap shot. In professional hockey, a slap shot is a type of shot in which a player literally “slaps” the puck with his stick. The puck may start with a very low speed and can leave the stick with
A car is outfitted with a flat piece of plywood mounted vertically on its front bumper. As seen in Figure P3.91, a block of wood is simply placed in front of the car just as the car begins to
Two spheres, one of balsa wood (diameter 40 cm) and one of steel (diameter 10 cm), have the same mass. (a) How many times greater is the terminal speed of the steel sphere than that of the
A block of mass M1= 3.0 kg rests on top of a second block of mass M2- 5.0 kg, and the second block sits on a surface that is so slippery that the friction can be assumed to be zero (see Fig.
Launching satellites into space using rockets is expensive, prompting some engineers and scientists to consider firing satellites into space using what is essentially a very powerful gun. In one
A bullet of mass m = 10 g and velocity 300 m/s is shot into a block of wood that is firmly attached to the ground. The bullet comes to rest in the wood at a depth of 8.1 cm. (a) What was the
Consider a small sailboat with a triangular sail of height 10 m and width at the base of 5.0 m. (a) Assuming a wind speed of 15 mi/h relative to the boat and a wind direction perpendicular to
High dive. The cliff-divers of Acapulco are famous for diving from steep cliffs that overlook the ocean into places where the water is very shallow. (a) Suppose a cliff-diver jumps from a cliff
The pedestrian walkway on the Golden Gate Bridge is about 75 m above the water below. This bridge is (unfortunately) a popular spot for some unhappy people, who attempt to jump off. Ignore air drag
The surfaces where bones meet are lubricated by a fluid like substance, which makes the coefficient of friction between bones very small (see Table 3.2). What is the approximate lateral (i.e.,
A driver makes an emergency stop and inadvertently locks up the brakes of the car, which skids to a stop on dry concrete. Consider the effect of rain on this scenario. If the coefficients of kinetic
You are trying to slide a refrigerator across a horizontal floor. The mass of the refrigerator is 200 kg, and you need to exert a force of 350 N to make it just begin to move. (a) What is the
After struggling to move the refrigerator in Problem 41, you finally apply enough force to get it moving. What is the minimum force required to keep it moving with a constant velocity? Assume μK -
The coefficient of kinetic friction between a refrigerator (mass 100 kg) and the floor is 0.20, and the coefficient of static friction is 0.25. If you apply the minimum force needed to get the
Your moving company runs out of rope and hand trucks, so you are forced to push two crates along the floor as shown in Figure P3.39. The crates are moving at constant velocity, their masses are m1-
You are given the job of moving a refrigerator of mass 100 kg across a horizontal floor. The coefficient of static friction between the refrigerator and the floor is 0.45. What is the minimum force
A car is moving with a velocity of 20 m/s when the brakes are applied and the wheels lock (stop spinning). The car then slides to a stop in 40 m. Find the coefficient of kinetic friction between the
A hockey puck slides with an initial speed of 50 m/s on a large frozen lake. If the coefficient of kinetic friction between the puck and the ice is 0.030, what is the speed of the puck after 10 s?
Three blocks rest on a friction less, horizontal table (Fig. P3.36), with m1= 10 kg and m3= 15 kg. A horizontal force F - 110 N is applied to block 1, and the acceleration of all three blocks is
A bodybuilder configures a leg-press apparatus (Fig. P3.35) to a resistance of 1000 N (about 230 lb). She pushes the weight to her full extension and comes to rest. (a) What is the normal force
A tall strongman of mass m = 95 kg stands upon a scale while at the same time pushing on the ceiling in a small room. Draw a free-body diagram of the strongman (Fig. P3.34) and indicate all normal
Your friend’s car has broken down, and you volunteer to push it to the nearest repair shop, which is 2.0 km away. You carefully move your car so that the bumpers of the two cars are in contact and
A grand piano with three legs has a mass of 350 kg and is at rest on a level floor. (a) Draw a free-body diagram for the piano. Show the force of the floor on each leg as a separate force in
The table in Figure Q3.14 is now sitting in an elevator, with m1- 9.5 kg and m2- 2.5 kg. The normal force between the table and the bottom book is 70 N. Find the magnitude and direction of the
Two books of mass m1= 8.0 kg and m2= 5.5 kg are stacked on a table as shown in Figure Q3.14. Find the normal force acting between the table and the bottom book.Figure Q3.14 тp тy
Under siege. Twenty soldiers hold a long beam of heavy wood against a fortified castle door and attempt to push it open (Fig. P3.29). If each soldier is able to supply a forward force on the beam of
A book of mass 3.0 kg sits at rest on a horizontal table. What is the magnitude of the normal force exerted by the table on the book?
A person has a weight of 500 N. What is her mass?
A motivated mule can accelerate an empty cart of mass m = 180 kg from rest to 5.0 m/s in 10 s. If the cart is loaded with 540 kg of wood, how long will it take the mule to get the cart to 5.0 m/s?
You are a passenger (m = 110 kg) in an airplane that is accelerating on the runway, beginning to take off. The force between your back and your seat is 400 N. Starting from rest, how far does the
A rock is dropped from a tree of height 25 m into a lake (depth 5.0 m) below. After entering the water, the rock floats gently down through the water at a constant speed of 1.5 m/s to the bottom of
One end of a string is tied to the ceiling of an elevator, and the other end is tied to a rock (Fig. Q3.20). The elevator is moving in such a way that the tension in the string is zero. (a) What
An astronaut measures her mass and her weight on Earth and again when she reaches the Moon. Which one of these quantities changes as a result of this trip and which one does not? Explain.
In our discussion of the block and tackle in Figure 3.23, we claimed that when the right end of the string is lifted through a distance L, the body of the pulley is lifted a distance L/2. Give a
Imagine a skydiver who waits a long time before opening her parachute. For simplicity, assume she moves along a straight line. (a) In what direction is the skydiver moving (what is the direction of
Imagine that you are a passenger on the International Space Station. While on the station, you are “weightless” and so is everything else, including wrenches and furniture. Even though everything
Devise a block-and-tackle arrangement that amplifies the applied force by a factor of three.
Give an example of motion in which the acceleration and the velocity are in opposite directions.
You work for a moving company and are given the job of pulling two large boxes of mass m1= 120 kg and m2= 290 kg using ropes as shown in Figure P3.63. You pull very hard, and the boxes are
A car of mass 1200 kg is lowered onto a junk pile at the end of the cable of a large crane. If the car is accelerating downward at 0.20 m/s2, what is the tension in the cable?
A crate of mass 55 kg is attached to one end of a string, and the other end of the string runs over a pulley and is held by a person as in Figure 3.22A. If the person pulls with a force of 85 N, what
A cable attached to a block of mass 12 kg pulls the block along a horizontal floor at a constant velocity. If the tension in the cable is 5.0 N, what is the coefficient of kinetic friction between
You are standing across the street from a tall building when the top of the building (h = 80 m) is hit by lightning and a brick is knocked loose. You see the lightning strike and immediately see that
Your friend is an environmentalist who is living in a tree for the summer. You are helping provide her with food, and you do so by throwing small packages up to her tree house. If her tree house is
You are standing at the top of a deep, vertical cave and want to determine the depth of the cave. Unfortunately, all you have is a rock and a stopwatch. You drop the rock into the cave and measure
A roofing tile falls from rest off the roof of a building. An observer from across the street notices that it takes 0.43 s for the tile to pass between two windowsills that are 2.5 m apart. How far
A rock is dropped from a tall bridge into the water below. If the rock begins with a speed of zero and has a speed of 12 m/s just before it hits the water, what is the height of the bridge as
Two children are playing on a 150-m-tall bridge. One child drops a rock (initial velocity zero) at t - 0. The other waits 1.0 s and then throws a rock downward with an initial speed v0. If the two
A ball is thrown directly upward with an initial velocity of 15 m/s. If the ball starts at an initial height of 3.5 m, how long is the ball in the air? Ignore air drag.
An apple falls from a branch near the top of a tall tree. If the branch is 12 m above the ground, what is the apple’s speed just before it hits the ground?
Basketball on the Moon. If LeBron James can jump 1.5 m high on Earth, how high could he jump on the Moon (assume an indoor court), where g - 1.6 m/s2?
A squirrel is resting in a tall tree when it slips from a branch that is 50 m above the ground. It is a very agile squirrel and manages to land safely on another branch after only 0.50 s. What is the
A baseball is hit directly upward with an initial speed of 45 m/s. Find the velocity of the ball when it is at a height of 40 m. Is there one correct answer for v or two? Explain why.
A rock is dropped from a very tall tower. If it takes 4.5 s for the rock to reach the ground, what is the height of the tower?
A hockey puck slides along a rough, icy surface. It has an initial velocity of 35 m/s and slides to a stop after traveling a distance of 95 m. Find the coefficient of kinetic friction between the
Anti lock brakes. A car travels at 65 mi/h when the brakes are suddenly applied. Consider how the tires of a moving car come in contact with the road. When the car goes into a skid (with wheels
Jeff Gordon (a race car driver) discovers that he can accelerate at 4.0 m/s2 without spinning his tires, but if he tries to accelerate more rapidly, he always “burns rubber.” (a) Find the
A ball is thrown upward with a speed of 35 m/s from the edge of a cliff of height h - 15 m (similar to Fig. P3.22). (a) What is the speed of the ball when it passes by the cliff on its way down
A bullet is fired upward with a speed v0from the edge of a cliff of height h (Fig. P3.22).(a) What is the speed of the bullet when it passes by the cliff on its way down? (b) What is the speed
A car is traveling at 25 m/s when the driver spots a large pothole in the road a distance 30 m ahead. She immediately applies her brakes. If her acceleration is -27 m/s2, does she manage to stop
Your car is initially traveling at a speed of 25 m/s. As you approach an intersection, you spot a dog in the road 30 m ahead and immediately apply your brakes. (a) If you stop the instant before
To measure the height of a tree, you throw a rock directly upward, with a speed just fast enough that the rock brushes against the uppermost leaves and then falls back to the ground. If the rock is
A barge on a still lake is moving toward a bridge at 10.0 m/s. When the bridge is 40.0 m away, the pilot slows the boat with a constant acceleration of -0.73 m/s2. (a) Use Equation 3.3 to find

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