Question 1

A person ties a rock to a string and whirls it around in a vertical circle such that sometimes the rock is going straight upward and sometimes the rock is going straight down.She whirls the rock at the minimum speed (constant in time)such that the string is always taut (no sag).When is the tension the highest?
A)It is highest when the rock is at the lowest elevation.
B)It is highest when the rock is at the highest elevation.
C)The tension is constant as the rock moves around in a circle.

Accepted Answer

The tension is highest when the rock is at the lowest elevation because, at this point, the gravitational force and the centripetal force both act in the same direction, increasing the tension in the string.

Question 2

A satellite having orbital speed V orbits a planet of mass M.If the planet had half as much mass,the orbital speed of the satellite would be:
A)V 
B)2V
C)V
D)V/ 
E)V/2

Accepted Answer

The answer of A satellite having orbital speed V orbits...

Question 3

A satellite of mass M takes time T to orbit a planet.If the satellite had twice as much mass,the time for it to orbit the planet would be:
A)4T
B)2T
C)T
D)T/2
E)T/4

Accepted Answer

According to Kepler's third law, the time period of a satellite orbiting a planet is proportional to the square root of the cube of the semi-major axis of the orbit. The mass of the satellite does not affect the time period. Therefore, if the mass of the satellite is doubled, the time period will remain the same. Hence the answer is C)T.

Question 4

For astronauts in space,there is no atmosphere to slow their orbit.Why don't they just fly away to the moon?

Accepted Answer

The answer of For astronauts in space,there is no atmosphere...

Question 5

If Earth had twice as much mass as it now does but were also twice its present diameter,the acceleration due to gravity at its surface would be the same as it is now.

Accepted Answer

The answer of If Earth had twice as much mass...

Question 6

Can a satellite be in an elliptical orbit under uniform circular motion?

Accepted Answer

The answer of Can a satellite be in an elliptical...

Question 7

A person ties a rock to a string and whirls it around in a vertical circle such that sometimes the rock is going straight upward and sometimes the rock is going straight down.She whirls the rock at the minimum speed (constant in time)such that the string is always taut (no sag).If she were to use a longer string,she would have to whirl the rock at a
A)higher velocity.
B)lower velocity.
C)the same velocity.

Accepted Answer

A longer string increases the radius of the circle, requiring a higher velocity to maintain the necessary centripetal force to keep the string taut.

Question 8

If you stood on a planet having a mass four times higher than Earth's mass,and a radius two times longer than Earth's radius,you would weigh
A)the same as you do on Earth.
B)two times more than you do on Earth.
C)two times less than you do on Earth.
D)four times more than you do on Earth.

Accepted Answer

Weight on a planet is given by W = (G * m1 * m2) / r^2, where G is the gravitational constant, m1 is the mass of the planet, m2 is the mass of the object, and r is the radius of the planet. If the mass of the planet is four times higher than Earth's mass and the radius is two times longer than Earth's radius, then the weight on the planet would be (4 * m1 * m2) / (2 * r)^2 = m1 * m2 / r^2, which is the same as the weight on Earth.

Question 9

If the Moon were twice the distance from Earth than it currently is,the amount of time it would take to go around Earth would be roughly (the current orbital period of the Moon is four weeks)
A)11 weeks.
B)eight weeks.
C)six weeks.
D)88 weeks.

Accepted Answer

The orbital period of a satellite is proportional to the 3/2 power of its orbital radius (Kepler's Third Law). If the Moon's distance is doubled, the period increases by a factor of 2^(3/2), which is approximately 2.83. Multiplying the current period (4 weeks) by 2.83 gives roughly 11 weeks.

Question 10

If an astronaut were exactly half way between Earth and the Moon,the net gravitational force exerted on the astronaut by these two objects would be
A)directed toward Earth.
B)zero.
C)directed toward the Moon.

Accepted Answer

The gravitational force exerted by Earth is stronger than that exerted by the Moon because Earth has a much larger mass. Therefore, even at the halfway point, the net gravitational force would be directed toward Earth.

Question 11

You need to make a sharp turn on a flat road,making a radius of curvature of 15 meters.How does the required force of static friction between your tires compare if you make the turn at 30 mph vs.60 mph?
A)The force of friction needs to be four times as large.
B)The force of friction needs to be twice as large.
C)The force of friction is the same for both speeds since the radius of curvature is the same.
D)None of the above

Accepted Answer

The force of static friction required for a turn is proportional to the square of the speed. Doubling the speed from 30 mph to 60 mph requires four times the force of friction.

Question 12

A mass on a string is swung in a vertical circle at a constant speed.The string will break if the tension in the string exceeds a critical value.At what part of the circle is the string most likely to break,and why?

Accepted Answer

The answer of A mass on a string is swung...

Question 13

Astronauts in orbit are weightless,but they are not beyond the pull of Earth's gravity.How can this be?

Accepted Answer

The answer of Astronauts in orbit are weightless,but they are...

Question 14

Explain,from a force standpoint,why you need to reduce your normal driving speed around curves when it rains.

Accepted Answer

The answer of Explain,from a force standpoint,why you need to...

Question 15

If the mass of Earth and all objects on it were suddenly doubled,the acceleration due to gravity at the surface would become 4 times what it is now.

Accepted Answer

The acceleration due to gravity is determined by the mass of the Earth and the distance from the center of the Earth to the object. If both the mass of the Earth and all objects on it were doubled, but the distance from the center of the Earth to the surface stayed the same, the acceleration due to gravity at the surface would not change.

Question 16

How is it possible for someone to remain in her seat (without any straps)while upside down on a loop-the-loop roller coaster?

Accepted Answer

The answer of How is it possible for someone to...

Question 17

In uniform circular motion we have an acceleration and the speed doesn't change.But in projectile motion the speed does change under constant acceleration.Why are they both classified as uniform acceleration phenomena?

Accepted Answer

The answer of In uniform circular motion we have an...

Question 18

If I set the car cruise control at a certain speed and take a turn,the speed will remain the same.So,why am I accelerating?

Accepted Answer

The answer of If I set the car cruise control...

Question 19

If there is no such thing as a centrifugal force,why does someone in a car making a turn feel as if he or she is being pulled toward the outside of the curve?

Accepted Answer

The answer of If there is no such thing as...

Question 20

A merry-go-round is spinning at a fixed rate.As a person is walking toward the edge,
A)the force of static friction must increase in order for the person not to slide off.
B)the force of static friction must decrease in order for the person not to slide off.
C)the force of static friction such that the person does not slide off remains the same.

Accepted Answer

As the person moves toward the edge, the centripetal force required to keep them moving in a circle increases, which means the force of static friction must increase to prevent them from sliding off.

Quiz 6: Circular Motion,orbits,and Gravity

A satellite having orbital speed V orbits a planet of mass M.If the planet had half as much mass,the orbital speed of the satellite would be:

A satellite of mass M takes time T to orbit a planet.If the satellite had twice as much mass,the time for it to orbit the planet would be:

For astronauts in space,there is no atmosphere to slow their orbit.Why don't they just fly away to the moon?

If Earth had twice as much mass as it now does but were also twice its present diameter,the acceleration due to gravity at its surface would be the same as it is now.

Can a satellite be in an elliptical orbit under uniform circular motion?

If you stood on a planet having a mass four times higher than Earth's mass,and a radius two times longer than Earth's radius,you would weigh

If the Moon were twice the distance from Earth than it currently is,the amount of time it would take to go around Earth would be roughly (the current orbital period of the Moon is four weeks)

If an astronaut were exactly half way between Earth and the Moon,the net gravitational force exerted on the astronaut by these two objects would be

You need to make a sharp turn on a flat road,making a radius of curvature of 15 meters.How does the required force of static friction between your tires compare if you make the turn at 30 mph vs.60 mph?