Downloadable Test Bank – How Things Work: The Physics of Everyday Life, 6th Edition (Louis A. Bloomfield)

4. To balance a baseball bat horizontally on one finger, where should the finger be placed?

• A) Just beneath the end of the handle
• B) Just beneath the opposite end
• C) Exactly halfway along the bat’s length
• D) Directly beneath the bat’s center of mass

5. A uniform seesaw is 4 m long and supported at its midpoint. A 20 kg child sits at one end, 2 m from the pivot. Where must her 100 kg father sit on the opposite side to keep the seesaw balanced?

• A) Beyond the end of the board
• B) 0.5 m from the pivot
• C) 0.4 m from the pivot
• D) 1.5 m from the pivot

6. While removing a wheel, a person places their entire weight of 800 N on the free end of a horizontal wrench. If the end is 2 m from the lug nut, what torque does the person apply?

• A) 1600 J
• B) 1600 N·m
• C) 800 N·m
• D) 2 N·m

7. A gravity-powered race car can use either solid-disk wheels or spoked wheels with most of their mass concentrated near the rim. Both sets have the same mass and radius. Why would the solid-disk wheels help the car accelerate more quickly downhill?

• A) Their smaller moment of inertia makes them easier to accelerate rotationally.
• B) Their surfaces are simpler to paint.
• C) Their larger moment of inertia allows them to retain more rotational energy.
• D) The spoked wheels waste excessive energy warming the surrounding air.

8. Earth rotates from west to east. Suppose a resistive torque acts to slow this rotation. According to the right-hand rule, in which direction does that torque point?

• A) Along the axis from the South Pole toward the North Pole
• B) Along the axis from the North Pole toward the South Pole
• C) Around the equator in a counterclockwise direction
• D) Around the equator in a clockwise direction

9. Imagine that the Moon takes twice as long to complete one rotation about its axis. If its moment of inertia stays constant, what happens to its rotational kinetic energy?

• A) It becomes twice its original value.
• B) It becomes four times its original value.
• C) It falls to one-quarter of its original value.
• D) It falls to one-half of its original value.

10. The Moon’s angular velocity decreases to half its initial value while its moment of inertia remains unchanged. What is its new rotational kinetic energy compared with its original value?

• A) Twice as much
• B) Four times as much
• C) One-quarter as much
• D) One-half as much

18. What allows an elastic ball to rebound effectively after striking a surface?

• A) It temporarily stores energy as it compresses and releases that energy as it regains its shape.
• B) It stores energy by remaining permanently deformed.
• C) Every elastic ball contains a special liquid that absorbs energy.
• D) Elastic balls always bounce well because they are thrown correctly.

19. During a collision, parts of a car’s body are designed to crumple permanently. Why does this reduce the car’s tendency to bounce back?

• A) The crumpled body stores the crash energy for later release.
• B) Permanent deformation dissipates energy from the collision.
• C) The deformation adds energy to the colliding objects.
• D) Crumpling increases the car’s coefficient of restitution.

20. A rubber ball falls onto a floor and then rebounds. What causes its motion to change from downward to upward?

• A) The ball must keep moving, and the floor prevents it from continuing downward.
• B) The ball’s own momentum remains constant throughout the impact.
• C) The ball’s own energy remains constant throughout the impact.
• D) The floor pushes upward on the ball, first stopping its downward motion and then accelerating it upward.

21. A tennis ball strikes a horizontal floor at an angle and rebounds. Ignoring friction during contact, which change occurs in its velocity?

• A) Its vertical component changes direction.
• B) Its horizontal component changes direction.
• C) Its speed changes to the opposite direction.
• D) Its vertical component becomes twice as large.

22. A ball with a coefficient of restitution of 0.45 strikes a stationary surface head-on at 100 m/s. At what speed does it rebound?

• A) 100 m/s
• B) 90 m/s
• C) 45 m/s
• D) 45 m/s²

23. An elastic ball drops onto the ground and bounces upward. At which instant does it contain the greatest amount of elastic potential energy?

• A) When it is most compressed and momentarily at rest before rebounding
• B) Just after it leaves the ground on the way up
• C) Immediately before it first touches the ground
• D) When it is traveling at its highest speed

24. A ball strikes a stationary wall head-on at 10 m/s and rebounds at 7 m/s. What is the coefficient of restitution for this collision?

• A) 1.41
• B) 0.70
• C) 0.49
• D) −17 m/s

25. A bat traveling at 90 km/h meets a ball approaching directly from the opposite direction at 110 km/h. The bat maintains its speed throughout the impact. If the coefficient of restitution is 0.6, how fast does the ball travel after being hit?

• A) 66 km/h
• B) 200 km/h
• C) 20 km/h
• D) 210 km/h