PHYSICS 151 EXAM 2 PRACTICE

When an object experiences uniform circular motion, the direction of the acceleration is

directed toward the center of the circular path.

An object moves in a circular path at a constant speed. Compare the direction of the object's velocity and acceleration vectors.

The vectors are perpendicular.

When an object experiences uniform circular motion, the direction of the net force is

directed toward the center of the circular path.

A car goes around a curve of radius r at a constant speed v. Then it goes around the same curve at half of the original speed. What is the centripetal force on the car as it goes around the curve for the second time, compared to the first time?

one-fourth as big

Two objects attract each other gravitationally. If the distance between their centers is cut in half, the gravitational force

quadruples.

Two objects, with masses m1 and m2, are originally a distance r apart. The gravitational force between them has magnitude F. The second object has its mass changed to 2m2 and the distance is changed to r/4. What is the magnitude of the new gravitational force?

32F

A spaceship is traveling to the Moon. At what point is it beyond the pull of Earth's gravity?

It is never beyond the pull of Earth's gravity.

An astronaut goes out for a "space-walk" at a distance above the Earth equal to the radius of the Earth (r = 2R). What is her acceleration due to gravity?

g/4

What is the correct unit of work expressed in SI base units?

kg·m^2/s^2

If you push twice as hard against a stationary brick wall, the amount of work you do

remains constant at zero.

A person carries a 5.0-kg bag of groceries horizontally across a level floor for 10 m at a constant speed. How much work is done on the groceries by the upward normal force of the person's hands?

0 J

If the net work done on an object is positive, then the object's kinetic energy

increases.

If the net work done on an object is negative, then the object's kinetic energy

decreases.

A car goes from speed v to 2v. By what factor does its stopping distance increase, assuming the braking force remains the same?

4

A truck weighs twice as much as a car, and is moving at twice the speed of the car. Which statement is true regarding their kinetic energies?

The truck has 8 times the kinetic energy of the car.

The area under the curve on a Force versus position (F vs. x) graph represents

work.

What is the SI unit of linear momentum?

kg·m/s

A rubber ball and a lump of clay of equal mass are thrown with equal speeds against a brick wall. The clay sticks to the wall, while the ball bounces backward. Which object experiences the greater impulse from the wall?

The rubber ball.

In an elastic collision between two isolated bodies, which of the following quantities are conserved?

Both kinetic energy and momentum.

In a completely inelastic collision between two objects, which quantity is NOT conserved?

Kinetic energy.

A small car crashes head-on into a large truck. Which vehicle experiences the greater force during the collision, and which experiences the greater acceleration?

Both experience equal force; car experiences greater acceleration.

A child sits on a carousel rotating at a constant angular speed. A second child sits twice as far from the center axis. Which child has the greater tangential speed (v)?

The child farther from the center.

For the two children in the previous question, which child has the greater angular speed (w)?

Both have the exact same angular speed.

When a net external torque acts on a rigid body, it produces a(n)

angular acceleration.

A force is applied to a wrench to turn a bolt. To maximize the applied torque, the force should be applied

at the very end of the handle, perpendicular (90°) to the wrench.

The acceleration due to gravity is lower on the Moon than on Earth. Which one of the following statements is true about the mass and weight of an astronaut on the Moon's surface, compared to Earth?

Mass is the same, weight is less.

Two men, Joel and Jerry, push against a car that has stalled, trying unsuccessfully to get it moving. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do on the car.

Neither of them does any work.

Two frisky otters slide down frictionless hillsides of the same height but different slopes. The slope of the hill of otter 1 is 30°, while the slope of the hill of otter 2 is 60°. If both start from rest, which otter is moving faster when she reaches the bottom of her hill?

Both otters have the same speed at the bottom.

You are standing on a skateboard, initially at rest. A friend throws a very heavy ball towards you. You have two choices about what to do with the ball: either catch the ball or deflect it back toward your friend with the same speed as it was originally thrown. Which choice should you make in order to maximize your speed on the skateboard?

Deflect the ball back.

A 30-N box is pulled upward 6.0 m along the surface of a ramp that rises at 37° above the horizontal. How much work does gravity do on the box during this process?

-110 J

A rubber ball and a lump of clay 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 clay sticks to the wall. Which one of these objects experiences the greater force?

the ball

Alex throws a 0.25-kg rubber ball down onto the floor. The ball's speed just before impact is 4.5 m/s, and just after is 2.9 m/s. What is the change in the magnitude of the ball's momentum?

1.9 kg⋅m/s

In an automobile collision, how does an airbag lessen the blow to the passenger? Assume as a result of the collision, the passenger stops.

The stopping impulse is the same for either the hard objects or the airbag. Unlike the windshield or dashboard, the air bag increases the time for the slowing process and thus decreases the average force on the passenger.

In a system with two moving objects, when a collision occurs between the objects:

the total momentum is always conserved.

A car is going around a racetrack at constant speed. The curves around the track have different radii. In which turn is the magnitude of the car's acceleration the greatest?

It is the greatest in the turn with the smallest radius.

In order to train for a high-g environment, an astronaut is placed in a centrifuge of radius several meters and rotated in a horizontal circle at constant speed. In this situation, in which direction is the net force on the astronaut?

The net force is horizontal toward the center of the circle.

Two objects with masses m1 and m2 are separated by a distance r. According to Newton's Law of Gravitation, if the distance between the objects is doubled, the gravitational force between them will:

Be reduced to one-fourth

Which of the following statements is correct about the acceleration due to gravity on different planets?

It depends on both the mass and radius of the planet.

Kepler's First Law states that:

The orbit of a planet around the Sun is an ellipse, with the Sun at one focus.

According to Kepler's Second Law, when a planet is closer to the Sun in its elliptical orbit, it:

Moves faster than when it is farther away.

What is the proper banking angle for an Olympic bobsled to negotiate a 100-m radius turn at 35 m/s without skidding (ignore friction)

51°

A highway curve of radius 100 m, banked at an angle of 45°, what's the maximum safest speed (ignore friction)?

31 m/s.

When an object moves in uniform circular motion, the direction of its acceleration is

is directed toward the center of its circular path.