Question 1

You can safely stand on the overhanging end of a heavy plank that rests on a table. How much overhang depends on your mass and the mass of the plank. If you can stand on the end of a plank that overhangs the edge of the supporting table 1/5 its total length, how massive is the plank compared to your mass?
A)1/3
B)the same
C)2/3
D)1 and 1/3 times
E)more than 1 and 1/3 times

Accepted Answer

The answer of You can safely stand on the overhanging...

Question 2

Centrifugal forces are an apparent reality to observers in a reference frame that is
A)moving at constant velocity.
B)an inertial reference frame.
C)at rest.
D)rotating.
E)none of the above

Accepted Answer

Centrifugal forces are a result of rotating reference frames, as objects in such frames experience apparent forces directed outwards from the axis of rotation. Only choice D, rotating, describes such a reference frame.

Question 3

If Earth rotated more slowly about its axis, your weight would
A)increase.
B)decrease.
C)stay the same.
D)be zero.

Accepted Answer

If Earth rotated more slowly, the centrifugal force would decrease, causing your effective weight to increase.

Question 4

You can safely stand on the overhanging end of a heavy plank that rests on a table. How much overhang depends on your mass and the plank's mass. If you can stand on the end of a plank that overhangs the edge of the supporting table 1/4 its total length, how massive is the plank compared to your mass?
A)1/2
B)the same
C)1 and 1/2 times
D)twice
E)4 times

Accepted Answer

Since you can safely stand on the end of the plank that overhangs 1/4 of its length, it means that the center of mass of the plank is still over the table, ensuring stability. This implies that the mass of the plank must be distributed uniformly. If the mass of the plank were greater than your own mass, the center of mass would be further away from the table, making it less stable and unsafe to stand on the overhanging end. Therefore, the mass of the plank must be the same as your mass for it to remain stable with an overhang of 1/4 of its length.

Question 5

The center of mass of a human body is located at a point that
A)is fixed, but different for different people.
B)is always directly behind the belly button.
C)changes as a person bends over.
D)none of the above

Accepted Answer

The center of mass of a human body changes as a person moves or changes posture, such as bending over.

Question 6

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

Accepted Answer

The long, heavy tail of a spider monkey helps the monkey in maintaining its balance by acting as a counterbalance. By moving its tail, the monkey can easily shift its center of gravity, allowing it to move and climb through trees with ease without falling. Therefore, the tail helps in varying the monkey's center of gravity.

Question 7

A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 12.5-cm mark. From this information, the mass of the meterstick is
A)1/4 kg.
B)1/2 kg.
C)3/4 kg.
D)1 kg.
E)none of the above

Accepted Answer

The answer of A 1-kg rock is suspended from the...

Question 8

Which of these has its center of mass where no mass exists?
A)baseball
B)golf ball
C)basketball
D)none of the above

Accepted Answer

A basketball is hollow, so its center of mass is located at the geometric center, where there is no material.

Question 9

Strictly speaking, to weigh less in the Northern Hemisphere, you should move to a location farther
A)north (toward the pole).
B)south (toward the equator).
C)east.
D)west.

Accepted Answer

The closer you are to the equator, the farther away you are from the Earth's axis of rotation, which causes a slight centrifugal force that reduces the apparent weight. Therefore, moving south (toward the equator) would make you weigh less in the Northern Hemisphere.

Question 10

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

Accepted Answer

The center of mass is the point where the mass of the object is evenly distributed, and it is the point around which the object will rotate in the absence of any external forces. Therefore, the baseball bat will wobble about its center of mass, which is a better choice than the geometrical center or the heavier end.

Question 11

If you balance a broom horizontally on one finger, the center of gravity of the broom will be above your finger, closer to the bristles end than the handle end. If you saw the broom in two pieces at that point and weigh the two parts on a scale, you'll find that the heavier part is the
A)bristles part.
B)handle part.
C)both the same weight

Accepted Answer

The center of gravity of the broom is closer to the bristles end, indicating that this part of the broom has more weight. When the broom is sawn into two pieces at this point, the heavier part will be the bristles part.

Question 12

A solitary boy cannot balance on a seesaw with its fulcrum at its midpoint. If the fulcrum is moved to one-quarter the distance from the boy, balance is achieved when the weight of the boy is
A)less than the weight of the seesaw.
B)equal to the weight of the seesaw.
C)more than the weight of the seesaw.
D)need more information

Accepted Answer

When the fulcrum is moved closer to the boy, it allows the boy's weight to balance out the seesaw by applying his weight over a shorter distance, effectively requiring his weight to be more than the seesaw's weight distributed over the longer distance to achieve balance.

Question 13

If Earth had a pair of identical moons on opposite sides of the same circular orbit, the center of gravity of the double-moon-Earth system would be
A)inside the Earth, but off center.
B)at the center of the Earth.
C)outside the Earth, but within the orbital path of the moons.
D)outside the Earth, but beyond the orbital path of the moons.

Accepted Answer

The center of gravity of the double-moon-Earth system would be at the exact center of the Earth, as the forces exerted by the two moons would cancel each other out, resulting in no net gravitational influence on the Earth's center.

Question 14

A boy plays solitary seesaw by placing the seesaw's fulcrum one-eighth the distance from where he sits at one end. Which weighs more?
A)the boy
B)the seesaw
C)they have equal weights
D)need more information

Accepted Answer

The boy weighs more. By placing the fulcrum one-eighth the distance from his end, he effectively makes the seesaw act as a lever with a mechanical advantage. This means the boy's weight is distributed more efficiently to lift the seesaw, indicating he must weigh more to balance the seesaw under these conditions.

Question 15

The main reason a person weighs less at the equator than at the poles involves the
A)spin of the Earth.
B)influence of the Sun, Moon, and all the planets.
C)law of action and reaction.

Accepted Answer

The spin of the Earth causes a centrifugal force at the equator that counteracts the gravitational force, making a person weigh less. At the poles, there is no centrifugal force, so the gravitational force is stronger, resulting in a higher weight for a person. The influence of the Sun, Moon, and all the planets may have a subtle effect on the Earth's overall gravity, but it is not significant enough to cause a noticeable difference in weight between the equator and poles. The law of action and reaction (Newton's Third Law) is not directly relevant to this phenomenon.

Question 16

When riding at constant velocity on a Segway electric vehicle, your center of mass is
A)slightly in front of the point between wheels below.
B)slightly behind the point between wheels below.
C)directly above the point between wheels below.

Accepted Answer

When riding at constant velocity, the Segway is balanced, and the center of mass of the rider and the vehicle is directly above the point between the two wheels on the bottom. This is because the Segway uses a self-balancing mechanism to keep the rider upright, and the control system adjusts the angle of the platform to maintain stability.

Question 17

The force responsible for a car moving steadily along a no-friction icy banked curve is due to
A)centrifugal effects.
B)the normal force at right angles to the curved surface.
C)the radial component of the normal force.
D)none of the above

Accepted Answer

The radial component of the normal force provides the necessary centripetal force that allows the car to move in a circular path on the icy banked curve without slipping, as there is no friction to contribute to this force.

Question 18

A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 25-cm mark. From this information, the mass of the meterstick is
A)1/4 kg.
B)1/2 kg.
C)3/4 kg.
D)1 kg.
E)none of the above

Accepted Answer

The meterstick balances when the fulcrum is at the 25-cm mark, with a 1-kg rock suspended at the 0-cm mark. This means the torque produced by the rock is balanced by the torque produced by the meterstick's own weight. Since the rock is 25 cm from the fulcrum and the meterstick's center of mass (assuming it's uniform) would be at the 50-cm mark, or 25 cm from the fulcrum on the other side, the weights must be equal for balance. Therefore, the meterstick also has a mass of 1 kg.

Question 19

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

Accepted Answer

The Leaning Tower of Pisa doesn't topple over because its center of gravity is above a place of support, which in this case is the foundation of the tower. This keeps the tower stable despite its famous lean.

Question 20

To kick a football so it won't topple end over end, kick it so the force of impact extends
A)above its center of gravity.
B)through its center of gravity.
C)below its center of gravity.

Accepted Answer

To avoid the football toppling end over end after being kicked, the force of impact should pass through its center of gravity. When the center of gravity is directly opposed to the force applied to the ball, the ball won't begin to spin or turn end over end.

Quiz 8: Rotational Motion

Centrifugal forces are an apparent reality to observers in a reference frame that is

If Earth rotated more slowly about its axis, your weight would

The center of mass of a human body is located at a point that

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

A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 12.5-cm mark. From this information, the mass of the meterstick is

Which of these has its center of mass where no mass exists?

Strictly speaking, to weigh less in the Northern Hemisphere, you should move to a location farther

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

If you balance a broom horizontally on one finger, the center of gravity of the broom will be above your finger, closer to the bristles end than the handle end. If you saw the broom in two pieces at that point and weigh the two parts on a scale, you'll find that the heavier part is the

A solitary boy cannot balance on a seesaw with its fulcrum at its midpoint. If the fulcrum is moved to one-quarter the distance from the boy, balance is achieved when the weight of the boy is

If Earth had a pair of identical moons on opposite sides of the same circular orbit, the center of gravity of the double-moon-Earth system would be

A boy plays solitary seesaw by placing the seesaw's fulcrum one-eighth the distance from where he sits at one end. Which weighs more?

The main reason a person weighs less at the equator than at the poles involves the

When riding at constant velocity on a Segway electric vehicle, your center of mass is

The force responsible for a car moving steadily along a no-friction icy banked curve is due to

A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 25-cm mark. From this information, the mass of the meterstick is

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

To kick a football so it won't topple end over end, kick it so the force of impact extends