PHYSICS TEST #2 MULTIPLE CHOICE
A tire is rolling along a road, without slipping, with a velocity v. A piece of tape is attached to the tire. When the tape is opposite the road (at the top of the tire), its velocity with respect to the road is
2v
A puck moves on a horizontal air table. It is attached to a string that passes through a hole in the center of the table. As the puck rotates about the hole, the string is pulled downward very slowly and shortens the radius of rotation, so the puck gradually spirals in towards the center. By what factor will the puck's angular speed have changed when the string's length has decreased by 1/2?
4
Substance A has a density of 3.0 g/cm3 and substance B has a density of 4.0 g/cm3. In order to obtain equal masses of these two substances, the ratio of the volume of A to the volume of B will be equal to
4:3
Consider three drinking glasses. All three have the same area base, and all three are filled to the same depth with water. Glass A is cylindrical. Glass B is wider at the top than at the bottom, and so holds more water than A. Glass C is narrower at the top than at the bottom, and so holds less water than A. Which glass has the greatest liquid pressure at the bottom?
All three have equal non-zero pressure at the bottom.
How a ship floats is described in terms of
Archimedes' principle.
Salt water has greater density than fresh water. A boat floats in both fresh water and in salt water. Where is the buoyant force greater on the boat?
Buoyant force is the same in both.
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger centripetal acceleration?
Child A
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger tangential speed?
Child A
A boy and a girl are riding on a merry-go-round that is turning. The boy is twice as far as the girl from the merry-go-round's center. If the boy and girl are of equal mass, which statement is true about the boy's moment of inertia with respect to the axis of rotation?
His moment of inertia is 4 times the girl's
A dumbbell-shaped object is composed by two equal masses, m, connected by a rod of negligible mass and length r. If I1 is the moment of inertia of this object with respect to an axis passing through the center of the rod and perpendicular to it and I2 is the moment of inertia with respect to an axis passing through one of the masses we can say that
I1<I2
A Ping-Pong ball moving east at a speed of 4 m/s, collides with a stationary bowling ball. The Ping-Pong ball bounces back to the west, and the bowling ball moves very slowly to the east. Which object experiences the greater magnitude impulse during the collision?
Neither; both experienced the same magnitude impulse.
A heavy boy and a lightweight girl are balanced on a massless seesaw. If they both move forward so that they are one-half their original distance from the pivot point, what will happen to the seesaw? Assume that both people are small enough compared to the length of the seesaw to be thought of as point masses.
Nothing will happen; the seesaw will still be balanced.
The SI unit of pressure is
Pa,N/m^2,kg/(m/s^2)
The hydraulic lift is an application of
Pascal's Principle
Jacques and George meet in the middle of a lake while paddling in their canoes. They come to a complete stop and talk for a while. When they are ready to leave, Jacques pushes George's canoe with a force to separate the two canoes. What is correct to say about the final momentum and kinetic energy of the system?
The final momentum is zero kgm/s but the final kinetic energy is positive.
A tennis ball undergoes an elastic collision when it hits the ground and bounces up. It is given that the speed of the ball just before it hits the ground is -v0 and immediately after rebounding it is +v0. Which of the statements below is true?
The momentum of the ball changes and the momentum of Earth also changes by the same amount.
A small car has a head-on collision with a large truck. Which of the following statements concerning the magnitude of the average force due to the collision is correct?
The small car and the truck experience the same average force.
A 3.0-kg object moves to the right at 4.0 m/s. It collides head-on with a 6.0-kg object moving to the left at 2.0 m/s. Which statement is correct?
The total momentum both before and after the collision is zero.
Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger angular speed?
They have the same non-zero angular speed.
In a collision between two objects having unequal masses, how does magnitude of the impulse imparted to the lighter object by the heavier one compare with the magnitude of the impulse imparted to the heavier object by the lighter one?
both objects receive the same impulse
In a perfectly ELASTIC collision between two perfectly rigid objects
both the momentum and the kinetic energy of the system are conserved.
You are standing on a skateboard, initially at rest. A friend throws a very heavy ball towards you. You can either catch the object or deflect the object back towards your friend (such that it moves away from you with the same speed as it was originally thrown). What should you do in order to MINIMIZE your speed on the skateboard?
catch the ball
A figure skater is spinning slowly with arms outstretched. She brings her arms in close to her body and her angular speed increases dramatically. The speed increase is a demonstration of
conservation of angular momentum: her moment of inertia is decreased, and so her angular speed must increase to conserve angular momentum.
Bernoulli's principle is a statement of the
conservation of energy
Identical forces act for the same length of time on two different masses. The change in momentum of the smaller mass is
equal to the change in momentum of the larger mass.
A system that has zero momentum must also have zero kinetic energy.
false
If two forces of equal magnitude act on an object that is hinged at a pivot, the force acting farther from the pivot must produce the greater torque about the pivot.
false
There must be equal amounts of mass on both side of the center of mass of an object
false
When a rigid body rotates about a fixed axis all the points in the body have the same tangential speed.
false
What is the difference between the pressures inside and outside a tire called?
gauge pressure
A flask of water rests on a scale. If you dip your finger into the water, without touching the flask, the reading on the scale will
increase
A railroad car of mass m and speed v collides and sticks to an identical railroad car that is initially at rest. After the collision, the kinetic energy of the system
is half as much as before
A freight car moves along a frictionless level railroad track at constant speed. The freight car is open on top. A large load of coal is suddenly dumped into the car. What happens to the speed of the freight car?
it decreases
When atmospheric pressure changes, what happens to the absolute pressure at the bottom of a pool?
it increases by the same amount
Salt water is more dense than fresh water. A ship floats in both fresh water and salt water. Compared to the fresh water, the volume of water displaced in the salt water is
less
What is the quantity used to measure an object's resistance to changes in rotational motion?
moment of inertia
On a smooth horizontal floor, an object slides into a spring which is attached to another mass that is initially stationary. When the spring is most compressed, both objects are moving at the same speed. Ignoring friction, what is conserved during this interaction?
momentum and mechanical energy
You are standing at a bus stop holding an umbrella on a rainy day. While you wait for the bus the rain shower turns into hail. Compared to the rain, the number of hail "drops" hitting the umbrella per second, the mass of the "drops", and their speed all remain the same. The force you must exert to hold the umbrella in the hail is
more than the force required in the rain
Each of the three containers shown in Figure 15-1 weighs the same amount and is filled with water to the same level. All three have the same surface area in contact with the table. Which of the following statements are true? I) The pressure at the bottom surface of the container is the same for all three containers. II) The force exerted by the water on the bottom surface of the container is the same for all three containers. III) The force exerted by the container on the table is the same for all three containers.
only statements I and II are true
Water flows through a pipe. The diameter of the pipe at point B is larger than at point A. Where is the speed of the water greater?
point A
An artillery shell explodes in midair and breaks up into many fragments. Which of the following statements are true regarding conditions immediately before and immediately after the explosion: I. The total momentum of the fragments is equal to the original momentum of the shell. II. The total kinetic energy of the fragments is equal to the original kinetic energy of the shell.
statement I only
A metal bar is hanging from a hook in the ceiling when it is suddenly struck by a ball that is moving horizontally (see figure). The ball is covered with glue, so it sticks to the bar. During this collision
the angular momentum of the system (ball and bar) is conserved about the hook because neither the hook nor gravity exerts any torque on this system about the hook.
A rubber ball and a lump of putty have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The putty sticks to the wall. Which objects experiences the greater momentum change?
the ball
You have two identical pure silver ingots. You place one of them in a glass of water and observe it to sink to the bottom. You place the other in a container full of mercury and observe that it floats. Comparing the buoyant forces in the two cases you conclude that
the buoyant force in water is smaller than the that in mercury.
A merry-go-round spins freely when Janice moves quickly to the center along a radius of the merry-go-round. It is true to say that
the moment of inertia of the system decreases and the angular speed increases
A shell explodes into two fragments, one fragment 25 times heavier than the other. If any gas from the explosion has negligible mass, then
the momentum change of the lighter fragment is exactly the same as the momentum change of the heavier fragment.
In an INELASTIC collision between two object
the momentum of the system is conserved but the kinetic energy of the system is not conserved
Two equal forces are applied to a door. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force exerts the greater torque?
the second at the doorknob
The buoyant force acts through the center of mass of the displaced fluid.
true
The center of mass of an object does not have to be located within the object.
true
When a rigid body rotates about a fixed axis all the points in the body have the same angular displacement.
true
When a rigid body rotates about a fixed axis all the points in the body have the same angular speed.
true
