Physics Test 3 Concept Coach

If an angular momentum vector is pointing straight down, what is the direction of the corresponding rotation, when viewed from above?

Clockwise

Mechanics sometimes put a length of pipe over the handle of a wrench when trying to remove a very tight bolt. How does this make it easier for the mechanic to remove the bolt?

It increases the toque the mechanic can apply, without the need to exert a greater force.

Most day care centers have carpeted floors instead of tile floors. What does this imply about the relationship between collision time and padding?

Padding increases collision time

CHAPTER 8: A small force and a large force impart the same change in momentum. What does this imply about the time interval over which each force acts?

The time interval is grater for the small force.

You hold a barbell in a horizontal position. The barbell's center of mass is exactly mid-way between your two hands. A friend walks up and attaches a weight on the end near your left hand. How does the torque on the bar exerted by your left hand compare to the torque on the bar from your right hand if the bar remains horizontal and at rest?

The torque from the left hand is greater than the torque from the right hand.

True or False: The moment of inertia of a hoop that has a mass MM and a radius RR is greater than the moment of inertia of a disk that has the same mass and radius.

True

A fan blade is initially at rest. It then undergoes angular acceleration for 10s10s , at a constant rate of 10rad/s210rad/s2 . Which of the following equations gives the correct value for the angular velocity after 10s10s ?

(10 rad/s/s)(10 s)

Two pucks collide on an air hockey table and bounce off each other in opposite directions. Each puck has a mass of 0.2 kg. Puck 1 has an initial velocity of 10 m/s, and puck 2 has an initial velocity of −25 m/s. After the collision, puck 1 recoils with a velocity of −5 m/s. What is the final velocity of puck 2?

-10 m/s

In an elastic collision, an object with momentum 12 kg·m/s collides with another. The final momenta of each are 14 kg∙m/s and 16 kg∙m/s respectively. What was the initial momentum of the second object?

18 kgm/s

Most simple machines are used in such a way that the mechanical advantage is greater than one. For which of the following simple machines is this not always the case? 1. a nail puller 2. a wheelbarrow 3. a shovel 4. a crank 5. an inclined plane

3 only

Suppose you are playing billiards and you find yourself behind the eight ball. You want to hit the cue ball at the eighth ball, which is at rest, and have the cue ball bounce off at an angle of 40 degrees to the left of the initial direction you hit the cue ball. At what angle will the eight ball recoil?

50 degrees to the right

What approach would you use to solve problems involving 2 D collisions?

Choose a coordinate system and then break the momentum into components.

Suppose a child walks from the outer edge of a rotating merry-go round in towards the center of rotation. Does the angular velocity of the merry-go-round increase, decrease, or remain the same?

Increases

Tennis racquets have "sweet spots." If the ball hits a sweet spot then the player's arm is not jarred as much as it would be otherwise. How does the "sweet spot" change the impact time of the ball?

It increases the impact time.

What is the difference between momentum and impulse?

Momentum is the product of mass and velocity. Impulse is the change in momentum.

Yes or No: If the maximum force the biceps muscle can exert is 1000N1000N , can we pick up an object that weights 1000N1000N ?

No.

Which of the following statement(s) best describe(s) a non-rotating object in static equilibrium? 1. It has zero velocity and zero acceleration. 2. It has nonzero velocity and zero acceleration. 3. It has zero velocity and nonzero acceleration. 4. It has nonzero velocity and nonzero acceleration.

Statement 1

Which of the following systems is in stable equilibrium? 1. a skateboard at rest at the bottom of a U-shaped ramp 2. a ball at rest on the edge of a table 3. a quarter, at rest, balanced on its rim

Systems 1 and 3

Suppose a fireworks shell explodes, breaking into three large pieces for which air resistance is negligible. How is the motion of the center of mass affected by the explosion?

The motion of the center of mass continues along its original original trajectory.

Why doesn't a rapidly spinning toy gyroscope fall over?

The net external torque is horizontal and in a direction perpendicular to the angular momentum.

Two children at a park sit on opposite ends of a see-saw. The first child sits closer to the center of the see-saw. What is true about the children's weights if the see-saw is at rest with both ends off the ground?

The second child is lighter in weight than the first child.

An object that has a small mass and an object that has a large mass have the same momentum. Which object has the largest speed?

The small mass.

CHAPTER 10: True or False: In circular motion, a non-zero tangential acceleration changes only the magnitude of the velocity, but not its direction.

True

CHAPTER 9: True or False: A rotating body can be in one of the types of equilibrium.

True

True or False: An elastic collision is a collision that conserves energy.

True

True or False: An elastic collision is one that conserves the sum of the kinetic energies of the objects in the system.

True

True or False: In a collision, the change in the angular momentum and the net external torque are directly proportional.

True

True or False: In an inelastic collision, energy is not conserved.

True

True or False: In circular motion, the centripetal acceleration changes only the direction of velocity, but not its magnitude.

True

True or False: Momentum for a system can be conserved in one direction while not being conserved in another.

True

True or False: The forces applied by our muscles on our bones are usually several times larger than the forces we exert on the outside world with our limbs.

True

A ball is at rest at the highest point on a hill. Is the ball in equilibrium, and if so, what kind of equilibrium?

Yes, the ball is in unstable equilibrium.

Competitive divers pull their limbs in and curl up their bodies when they do somersaults. Just before entering the water, they fully extend their limbs to enter straight down. How does their angular velocity change when they fully extend their limbs?

decreases

The equations for the kinematics of rotational motion are most similar in form to which other set of equations?

kinematics of translational motion

Scissors are a type of simple machine. Which simple machine is most analogous to scissors?

lever

Two objects collide with each other and come to rest. How can you use the equation of conservation of momentum to describe this situation?

m1v1 + m2v2 = 0

Which combination equals the rotational work done on a spinning tire?

net torque on the tire times the tire's angle of the tire's displacement

A student is trying to reduce the mass of a racing bike to achieve greater acceleration. Would it be more beneficial to reduce the mass of the tires or reduce an identical mass from the bicycle's frame?

tires

Suppose a particle of known mass and velocity collides with a second particle of known mass that is at rest. You try to solve for the final velocities of both particles in the plane of collision, but when you apply the equations of conservation of momentum along the x-axis and y-axis, you realize that there are too many unknowns. How many pieces of information do you need to solve for each particle's final velocity?

two

A boy throws a yo-yo downward and watches it climb back up. As the yo-yo is going down, which types of energy are changing? 1. Translational kinetic energy 2. Rotational kinetic energy 3. Gravitational potential energy

types 1, 2, and 3