Questions and Answers of Physics Everyday Phenomena

Water emerges from a faucet at a speed of 1.5 m/s. After falling a short distance, its speed increases to 3 m/s as a result of the gravitational acceleration. By what number would you multiply the
A stream moving with a speed of 0.5 m/s reaches a point where the cross-sectional area of the stream decreases to one-fourth of the original area. What is the water speed in this narrowed portion of
A certain boat displaces a volume of 4.5 m3 of water. (The density of water is 1000 kg/m3.)a. What is the mass of the water displaced by the boat?b. What is the buoyant force acting on the boat?
A block of wood of uniform density floats so that exactly half of its volume is underwater. The density of water is 1000 kg/m3. What is the density of the block?
With the temperature held constant, the piston of a cylinder containing a gas is pulled out so that the volume increases from 0.1m3to 0.3m3. If the initial pressure of the gas was 80 kPa, what is the
With the temperature held constant, the pressure of a gas in a cylinder with a movable piston is increased from 10 kPa to 90 kPa. The initial volume of the gas in the cylinder is 0.36 m3. What is the
A column of water in a vertical pipe has a cross-sectional area of 0.2 m2 and a weight of 450 N. What is the increase in pressure (in Pa) from the top to the bottom of the pipe?
The load-bearing piston in a certain hydraulic system has an area 50 times as large as the input piston. If the larger piston supports a load of 6000 N, how large a force must be applied to the input
In a hydraulic system, a force of 400 N is exerted on a piston with an area of 0.001m2. The load-bearing piston in the system has an area of 0.2m2.a. What is the pressure in the hydraulic fluid?b.
The pressure of a gas contained in a cylinder with a movable piston is 450 Pa (450 N/m2). The area of the piston is 0.2 m2. What is the magnitude of the force exerted on the piston by the gas?
A 250-lb man supports all of his weight on a show shoe with an area of 200 in2. What pressure is exerted on the snow (in pounds per square inch)?
A force of 40 N pushes down on the movable piston of a closed cylinder containing a gas. The piston’s area is 0.5 m2. What pressure does this produce in the gas?
From the perspective of a right-handed batter, does a rising fastball spin clockwise or counterclockwise? Explain.
A hair dryer can be used to create a stream of air. Is the air pressure in the center of the stream greater than, less than, or equal to the air pressure at some distance from the center of the
A wind gust blows sideways across an outward-swinging door that is slightly ajar. Will this cause the door to slam shut or swing open? Explain.
If you blow between two limp pieces of paper held hanging down a few inches apart, will the pieces of paper come closer together or move farther apart? Explain.
Why is the flow of smoke from a cigarette often laminar near the source but turbulent farther from the source? Explain.
If the speed of flow in a stream decreases, is the flow likely to change from laminar to turbulent flow? Explain.
Does a stream of liquid with a high viscosity flow more rapidly under the same conditions as a stream with low viscosity? Explain.
Why does the stream of water flowing from a faucet often get more narrow as the water falls? Explain.
A steady stream of water flowing in a narrow pipe reaches a point where the pipe widens. Does the speed of the water increase, decrease, or remain the same when the pipe widens? Explain.
If an object has a smaller density than water, will the object stay fully submerged, partly submerged, or rise completely out of the water when it is released underwater? Explain.
A rowboat is floating in a swimming pool when the anchor is dropped over the side. When the anchor is dropped, will the water level in the swimming pool increase, decrease, or remain the same?
Is it possible that some objects might float in salt water but sink in fresh water? Explain.
A large bird lands on a rowboat that is floating in a swimming pool. Will the water level in the pool increase, decrease, or remain the same when the bird lands on the boat? Explain.
A block of wood is floating in a pool of water.a. Is the buoyant force acting on the block greater than, less than, or equal to the weight of the block? Explain.b. Is the volume of the fluid
Is it possible for a boat made of concrete to float? Explain.
A rectangular metal block is suspended by a string in a beaker of water so that the block is completely surrounded by water. Is the water pressure at the bottom of the block equal to, greater than,
Is it possible for a solid metal ball to float in mercury? Explain.
Helium is sealed inside a balloon impermeable to the flow of gas. If a storm suddenly comes up, would you expect the balloon to expand or contract? Explain. (Assume that there is no change in
The plunger of a sealed hypodermic syringe containing air is slowly pulled out. Does the air pressure inside the syringe increase or decrease when this happens? Explain.
When you go over a mountain pass in an automobile, your ears often “pop” both on the way up and on the way down. How can you explain this effect?
If you filled an airtight balloon at the top of a mountain, would the balloon expand or contract as you descend the mountain? Explain.
If you climbed a mountain carrying a mercury barometer, would the level of the mercury column in the glass tube of the barometer increase or decrease (compared to the mercury reservoir) as you climb
A blood pressure reading is given as 130/75.a. What units are implied by these numbers?b. Are these numbers total pressures or gauge pressures? Explain.
Could we use water instead of mercury to make a barometer? What advantages and disadvantages would be associated with the use of water? Explain.
When a mercury barometer is used to measure atmospheric pressure, does the closed end of the tube above the mercury column usually contain air? Explain.
If the output piston in a hydraulic pump exerts a greater force than one applied to the input piston, is the pressure at the output piston also larger than at the input piston? Explain.
The fluid in a hydraulic system pushes against two pistons, one with a large area and the other with a small area.a. Which piston experiences the greater force due to fluid pressure acting on it?
Why are bicycle tires often inflated to a higher pressure than automobile tires, even though the automobile tires must support a much larger weight? Explain.
A penny and a quarter are embedded in the concrete bottom of a swimming pool filled with water. Which of these coins experiences the greater downward force due to water pressure acting on it? Explain.
The same force is applied to two cylinders that contain air. One has a piston with a large area, and the other has a piston with a small area. In which cylinder will the pressure be greater? Explain
If we measure force in pounds (lb) and distance in feet (ft), what are the units of pressure in this system? Explain.
Is it possible for a 100-lb woman to exert a greater pressure on the ground than a 250-lb man? Explain.
A student sitting on a stool that is free to rotate but is initially at rest, holds a bicycle wheel. The wheel has a rotational velocity of 5 rev/s about a vertical axis, as shown in the diagram. The
In the park, several children with a total mass of 240 kg are riding on a merry-go-round that has a rotational inertia of 1500 kg·m2 and a radius of 2.2 m. The average distance of the children from
A 4-m long plank with a weight of 80 N is placed on a dock with 1 m of its length extended over the water, as in the diagram. The plank is uniform in density so that the center of gravity of the
A merry-go-round in the park has a radius of 1.8 m and a rotational inertia of 900 kg·m2. A child pushes the merry -go-round with a constant force of 80 N applied at the edge and parallel to the
A student, sitting on a stool rotating at a rate of 20 RPM, holds masses in each hand. When his arms are extended, the total rotational inertia of the system is 4.5 kg·m2. He pulls his arms in close
A uniform disk with a mass of 4 kg and a radius of 0.2 m is rotating with a rotational velocity of 20 rad/s.a. What is the rotational inertia of the disk? (See fig. 8.15.)b. What is the angular
A mass of 0.8 kg is located at the end of a very light and rigid rod 50 cm in length. The rod is rotating about an axis at its opposite end with a rotational velocity of 3 rad/s.a. What is the
Two 0.2-kg masses are located at either end of a 1-m long, very light and rigid rod as in the diagram. What is the rotational inertia of this system about an axis through the center of the rod?
A torque of 60 N·m producing a counterclockwise rotation is applied to a wheel about its axle. A frictional torque of 10 N·m acts at the axle.a. What is the net torque about the axle of the
A wheel with rotational inertia of 4.5 kgm2 accelerates at a rate of 3.0 rad/s2. What net torque is needed to produce this acceleration?
A net torque of 60 N·m is applied to a disk with rotational inertia of 12.0 kgm2. What is the rotational acceleration of the disk?
A weight of 3 N is located 10 cm from the fulcrum on the beam of a simple balance. What weight should be placed at a point 5 cm from the fulcrum on the opposite side in order to balance the system?
A weight of 30 N is located a distance of 10 cm from the fulcrum of a simple balance beam. At what distance from the fulcrum should a weight of 20 N be placed on the opposite side in order to balance
A force of 50 N is applied at the end of a wrench handle that is 24 cm long. The force is applied in a direction perpendicular to the handle as in the diagram.a. What is the torque applied to the nut
Starting from rest a merry-go-round accelerates at a constant rate of 0.2 rev/s2.a. What is its rotational velocity after 5 s?b. How many revolutions occur during this time?
The rotational velocity of a spinning disk decreases from 6 rev/s to 3 rev/s in a time of 12 s. What is the rotational acceleration of the disk?
A bicycle wheel is rotationally accelerated at the constant rate of 1.2 rev/s2.a. If it starts from rest, what is its rotational velocity after 4 s?b. Through how many revolutions does it turn in
The rotational velocity of a merry-go-round increases at a constant rate from 0.6 rad/s to 1.8 rad/s in a time of 4 s. What is the rotational acceleration of the merry-go-round?
Suppose that a disk rotates through three revolutions in 4 seconds.a. What is its displacement in radians in this time?b. What is its average rotational velocity in rad/s?
When the author was a teenager, the rate of rotation for popular music records on a record player was 45 RPM.a. Express this rotational velocity in rev/s.b. Through how many revolutions does the
Suppose that a merry-go-round is rotating at the rate of 10 rev/min.a. Express this rotational velocity in rev/s.b. Express this rotational velocity in rad/s
Can a yo-yo be made to “sleep” if the string is tied tightly to the axle? Explain.
A top falls over quickly if it is not spinning, but will stay approximately upright for some time when it is spinning. Explain why this is so.
A pencil, balanced vertically on its eraser, falls to the right.a. What is the direction of its angular-momentum vector as it falls?b. Is its angular momentum conserved during the fall? Explain.
An ice skater is spinning counterclockwise about a vertical axis when viewed from above. What is the direction of her angular-momentum vector? Explain.
Does the direction of the angular-momentum vector of the wheels change when a bicycle goes around a corner? Explain.
Suppose you are rotating a ball attached to a string in a circle. If you allow the string to wrap around your finger, does the rotational velocity of the ball change as the string shortens? Explain.
Is it possible for an ice skater to change his rotational velocity without involving any external torque? Explain.
Moving straight inward, a large child jumps onto a freely rotating merry-go-round. What effect will this have on the rotational velocity of the merry-go-round? Explain.
A child on a freely rotating merry-go-round moves from near the center to the edge. Will the rotational velocity of the merry-go-round increase, decrease, or not change at all? Explain.
A metal rod is rotated first about an axis through its center and then about an axis passing through one end. If the rotational velocity is the same in both cases, is the angular momentum also the
Is angular momentum always conserved? Explain.
A solid sphere and a hollow sphere made from different materials have the same mass and the same radius. Which of these two objects, if either, will have the greater rotational inertia about an axis
Can you change your rotational inertia about a vertical axis through the center of your body without changing your total weight? Explain.
Is it possible for two objects with the same mass to have different rotational inertias? Explain.
Two objects have the same total mass, but object A has its mass concentrated closer to the axis of rotation than object B. Which object will be easier to set into rotational motion? Explain.
A tall crate has a higher center of gravity than a shorter crate. Which will have the greater tendency to tip over if we push near the top of the crate? Explain with a force diagram. Where is the
An object is rotating with a constant rotational velocity. Can there be a net torque acting on the object? Explain.
A uniform metal wire is bent into the shape of an L. Will the center of gravity for the wire lie on the wire itself? Explain.
A solid plank with a uniform distribution of mass along its length rests on a platform with one end of the plank protruding over the edge. How far out can we push the plank before it tips? Explain.
A pencil is balanced on a fulcrum located two-thirds of the distance from one end. Is the center of gravity of this pencil located at its center point? Explain.
You are trying to move a large rock using a steel rod as a lever. Will it be more effective to place the fulcrum nearer to your hands or nearer to the rock? Explain.
Is it possible for the net force acting on an object to be zero, but the net torque to be greater than zero? Explain. (The forces contributing to the net force may not lie along the same line.)
Is it possible to balance two objects of different weights on the beam of a simple balance resting upon a fulcrum? Explain.
The two forces in the diagram have the same magnitude. Which orientation will produce the greater torque on the wheel? Explain. F, F2 Q11 Diagram
Which of the forces pictured as acting upon the rod in the diagram will produce a torque about an axis perpendicular to the plane of the diagram at the left end of the rod? Explain. Axis F2 Q10
Which, if either, will produce the greater torque: a force applied at the end of a wrench handle (perpendicular to the handle) or an equal force applied in the same direction near the middle of the
A ball rolls down an inclined plane gaining speed as it goes. Does the ball experience both linear and rotational acceleration? How far does the ball travel in one revolution? How is the linear
If an object has a constant rotational acceleration, is its rotational velocity also constant? Explain.
Is the linear speed of a child sitting near the center of a rotating merry-go-round the same as that of another child sitting near the edge of the same merry-go-round? Explain.
Is the rotational velocity of a child sitting near the center of a rotating merry-go-round the same as that of another child sitting near the edge of the same merry-go-round? Explain.
The rate of rotation of an object is gradually slowing down. Does this object have a rotational acceleration? Explain.
A coin rolls down an inclined plane gaining speed as it rolls. Does the coin have a rotational acceleration? Explain.
Which units would not be appropriate for describing a rotational acceleration: rad/s, rev/s2, rev/m2 , degrees/s2 ? Explain.
Which units would not be appropriate for describing a rotational velocity: rad/min2, rev/s, rev/h, m/s? Explain.
A 1500-kg car traveling due north with a speed of 25 m/s collides head-on with a 4500-kg truck traveling due south with a speed of 15 m/s. The two vehicles stick together after the collision.a. What

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