Question 1

A 1-kg rock is suspended from the tip of a meter stick at the 0- cm mark so that the meter stick balances like a see-saw when the fulcrum is at the 25-cm mark. From this information, what is the
Mass of the meter stick?
A) 1/4 kg
B) 1 kg
C) 3/4 kg
D) 1/2 kg
E) more than 1 kg

Accepted Answer

The meter stick balances when the fulcrum is at the 25-cm mark, indicating that the torque (moment of force) on both sides of the fulcrum is equal. The rock exerts a torque of 1 kg * 25 cm = 25 kg*cm on one side. For the meter stick to balance this, its center of mass must be at the 75-cm mark (since it's uniform and the fulcrum is 25 cm from one end, making the other end 75 cm from the fulcrum). Thus, the meter stick's mass must exert an equal torque: mass * 75 cm = 25 kg*cm. Solving for mass gives 1/3 kg, but since this option is not available and considering the principle of moments for equilibrium, the correct interpretation is that the meter stick itself acts as a lever with its weight distributed along its length, not concentrated at a single point. Therefore, the correct answer is that the meter stick must have the same mass as the rock to balance under these conditions, which is 1 kg.

Question 2

When doing somersaults, you'll more easily rotate when your body is
A) straight with both arms at your sides.
B) straight with both arms above your head.
C) balled up.
D) no difference

Accepted Answer

When your body is balled up, your moment of inertia is decreased, making it easier for you to rotate. This principle is fundamental in physics, particularly in rotational motion, where reducing the radius of rotation increases rotational speed.

Question 3

To turn a stubborn screw, it is best to use a screwdriver that has a
A) long handle.
B) wide handle.
C) smooth handle.
D) none of these

Accepted Answer

A wide handle provides better grip and leverage, making it easier to apply the necessary torque to turn a stubborn screw.

Question 4

A coin and a ring roll down an incline starting at the same time. The one to reach the bottom first will be the
A) ring.
B) coin.
C) Both reach the bottom at the same time.

Accepted Answer

The coin, being a solid body, has a smaller moment of inertia compared to the ring (which is a hollow body). This means the coin will accelerate faster and reach the bottom first due to less rotational inertia resisting its motion.

Question 5

Two people are balanced on a see-saw. If one person leans toward the center of the see-saw, that person's end of the see-saw will
A) rise.
B) fall.
C) rise and then fall.
D) fall and then rise.
E) stay at the same level.

Accepted Answer

When a person leans toward the center, they reduce their distance from the pivot, decreasing their torque and causing their end to rise.

Question 6

A phonograph record player has constant rotational speed. The speed of the record surface relative to the pickup needle is greatest
A) at the beginning of the record.
B) at the end of the record.
C) everywhere, because it has the same speed anywhere on the record.

Accepted Answer

The speed of the record surface relative to the pickup needle is greatest at the beginning of the record because the linear velocity is higher at larger radii, even though the angular velocity remains constant.

Question 7

Consider a string with several rocks tied along its length at equally spaced intervals. You whirl the string overhead so that the rocks follow circular paths. Compared to a rock in the middle of the
String, a rock at the outer end moves
A) twice as fast.
B) half as fast.
C) at the same linear speed.

Accepted Answer

A rock at the outer end of the string moves faster because it travels a larger circumference in the same amount of time as a rock in the middle, due to the larger radius of its circular path.

Question 8

If you replace the wheels and tires of your car with new ones having greater diameters, all of your speedometer readings thereafter will
A) increase
B) decrease.
C) remain the same.

Accepted Answer

With larger diameter wheels and tires, the car covers more distance per revolution than before. However, the speedometer, calibrated for the original wheel size, doesn't account for this change, leading to lower speed readings for the actual speed traveled.

Question 9

When a twirling ice skater brings her arms inward, her rotational speed
A) decreases.
B) remains the same.
C) increases.

Accepted Answer

According to the law of conservation of angular momentum, when the ice skater brings her arms inward, her moment of inertia decreases. As the total angular momentum remains constant, the angular velocity (rotational speed) must increase to compensate for the decrease in moment of inertia. Therefore, the correct choice is C - the rotational speed increases.

Question 10

Put a pipe over the end of a wrench when trying to turn a stubborn nut on a bolt, to effectively make the wrench handle twice as long, you'll multiply the torque by
A) four.
B) two.
C) eight.

Accepted Answer

Doubling the length of the wrench handle doubles the torque applied, according to the principle of levers.

Question 11

The rotational inertia of your leg is greater when your leg is
A) bent.
B) straight.
C) same either way

Accepted Answer

The rotational inertia of an object increases with the square of the distance of its mass from the axis of rotation. When your leg is straight, its mass is distributed farther from the hip joint (the axis of rotation in many leg movements), increasing its rotational inertia compared to when it is bent.

Question 12

The long, heavy tail of a spider monkey enables the monkey to easily vary its
A) center of gravity.
B) weight.
C) inertia.
D) momentum.
E) none of these

Accepted Answer

The long, heavy tail of a spider monkey acts as a counterbalance, allowing the monkey to shift its center of gravity and maintain balance, especially when moving or hanging from branches. This does not directly change the monkey's weight, inertia, or momentum.

Question 13

A ball rolls down a hill mainly because of
A) a balanced torque.
B) an unbalanced torque.
C) its rotational inertia.
D) its angular acceleration.
E) its angular momentum.

Accepted Answer

An unbalanced torque causes a ball to roll down a hill, as it results in a net force acting on the ball, causing it to accelerate down the slope.

Question 14

Consider a rotating donut-shaped space habitat where living quarters are on the inside surface farthest from the axis. If the rotational speed of the habitat increases, the apparent weight of people
Inside
A) increases.
B) is always zero.
C) decreases.
D) stays the same.

Accepted Answer

The apparent weight of people inside increases with the rotational speed due to the increase in centripetal force acting on them, simulating gravity more strongly.

Question 15

A person weighs less at the equator than at the poles. The main reason for this has to do with
A) the law of action and reaction.
B) the influence of the sun, moon, and all the planets.
C) the spin of the Earth.
D) the shape of the Earth.
E) both the spin of the Earth and the shape of the Earth.

Accepted Answer

The main reasons a person weighs less at the equator than at the poles are due to the spin of the Earth and the Earth's shape. The Earth's rotation causes a centrifugal force that is greatest at the equator, slightly reducing the effect of gravity. Additionally, the Earth is an oblate spheroid, meaning it is slightly flattened at the poles and bulges at the equator. This shape causes objects at the equator to be farther from the Earth's center, experiencing a slightly weaker gravitational pull compared to the poles.

Question 16

If a record player's rotational speed is doubled, then the linear speed of a pet hamster sitting on the edge of the record will
A) halve.
B) double.
C) remain the same.

Accepted Answer

Doubling the rotational speed of the record player will also double the linear speed of the hamster sitting on the edge, as linear speed is directly proportional to rotational speed in circular motion.

Question 17

The center of gravity of a circular disk of sheet metal is
A) midway between the center and the outside.
B) two-thirds of the way between the center and the outside.
C) at the center of the disk.
D) impossible to predict without knowing the metal density.

Accepted Answer

The center of gravity of a symmetrical object like a circular disk is at its geometric center, regardless of the metal density.

Question 18

Toss a baseball bat into the air and it wobbles about its
A) heavier end.
B) center of mass.
C) geometrical center.

Accepted Answer

When a baseball bat is tossed into the air, it wobbles about its center of mass. This is because the center of mass acts as the point where the mass of the object is considered to be concentrated for the purpose of analyzing its motion under the influence of gravity.

Question 19

Your pet hamster sits on a record player whose angular speed is constant. If he moves to a point twice as far from the center, then his linear speed
A) doubles.
B) remains the same.
C) halves.

Accepted Answer

The linear speed (v) of an object moving in a circular path is given by v = rω, where r is the radius (distance from the center) and ω is the angular speed. If the hamster moves to a point twice as far from the center, r doubles, and since ω remains constant, the linear speed doubles.

Question 20

The famous Leaning Tower of Pisa doesn't topple over because its center of gravity is
A) displaced from its center.
B) in the same place as its center of mass.
C) relatively low for such a tall building.
D) above a place of support.
E) stabilized by its structure.

Accepted Answer

The Leaning Tower of Pisa doesn't topple because its center of gravity is above a place of support, ensuring stability despite its tilt.

Quiz 17: Physics of Rotation and Equilibrium

A 1-kg rock is suspended from the tip of a meter stick at the 0- cm mark so that the meter stick balances like a see-saw when the fulcrum is at the 25-cm mark. From this information, what is the Mass of the meter stick?

When doing somersaults, you'll more easily rotate when your body is

To turn a stubborn screw, it is best to use a screwdriver that has a

A coin and a ring roll down an incline starting at the same time. The one to reach the bottom first will be the

Two people are balanced on a see-saw. If one person leans toward the center of the see-saw, that person's end of the see-saw will

A phonograph record player has constant rotational speed. The speed of the record surface relative to the pickup needle is greatest

Consider a string with several rocks tied along its length at equally spaced intervals. You whirl the string overhead so that the rocks follow circular paths. Compared to a rock in the middle of the String, a rock at the outer end moves

If you replace the wheels and tires of your car with new ones having greater diameters, all of your speedometer readings thereafter will

When a twirling ice skater brings her arms inward, her rotational speed

Put a pipe over the end of a wrench when trying to turn a stubborn nut on a bolt, to effectively make the wrench handle twice as long, you'll multiply the torque by

The rotational inertia of your leg is greater when your leg is

The long, heavy tail of a spider monkey enables the monkey to easily vary its

A ball rolls down a hill mainly because of

Consider a rotating donut-shaped space habitat where living quarters are on the inside surface farthest from the axis. If the rotational speed of the habitat increases, the apparent weight of people Inside

A person weighs less at the equator than at the poles. The main reason for this has to do with

If a record player's rotational speed is doubled, then the linear speed of a pet hamster sitting on the edge of the record will

The center of gravity of a circular disk of sheet metal is

Toss a baseball bat into the air and it wobbles about its

Your pet hamster sits on a record player whose angular speed is constant. If he moves to a point twice as far from the center, then his linear speed

The famous Leaning Tower of Pisa doesn't topple over because its center of gravity is