Tossing Balls off a Cliff Learning Goal: To clarify the distinction between spee

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Tossing Balls off a Cliff

Learning Goal:

To clarify the distinction between speed and velocity, and to review qualitatively one-dimensional kinematics.

For the following questions neglect air resistance. Pay particular attention to whether the answer involves "absolute" quantities that have only magnitude (e.g., speed) or quantities that can have either sign (e.g., velocity). Take upward to be the positive direction.

Part A

If the ball that is thrown downward has an acceleration of magnitude a at the instant of its release (i.e., when there is no longer any force on the ball due to the woman's hand), what is the relationship between a and g, the magnitude of the acceleration of gravity?

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Part B

Which ball has the greater acceleration at the instant of release?

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Part C

Which ball has the greater speed at the instant of release?

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Part D

Which ball has the greater average speed during the 1-s interval after release (assuming neither hits the ground during that time)?

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Part E

Which ball hits the ground with greater speed?

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Tossing Balls off a Cliff

Learning Goal:

To clarify the distinction between speed and velocity, and to review qualitatively one-dimensional kinematics.

A woman stands at the edge of a cliff, holding one ball in each hand. At time t0, she throws one ball straight up with speed v0 and the other straight down, also with speed v0.

For the following questions neglect air resistance. Pay particular attention to whether the answer involves "absolute" quantities that have only magnitude (e.g., speed) or quantities that can have either sign (e.g., velocity). Take upward to be the positive direction.

Part A

If the ball that is thrown downward has an acceleration of magnitude a at the instant of its release (i.e., when there is no longer any force on the ball due to the woman's hand), what is the relationship between a and g, the magnitude of the acceleration of gravity?

If the ball that is thrown downward has an acceleration of magnitude  at the instant of its release (i.e., when there is no longer any force on the ball due to the woman's hand), what is the relationship between  and , the magnitude of the acceleration of gravity? a>g a=g a<g

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Part B

Which ball has the greater acceleration at the instant of release?

Which ball has the greater acceleration at the instant of release? the ball thrown upward the ball thrown downward Neither; the accelerations of both balls are the same.

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Part C

Which ball has the greater speed at the instant of release?

Which ball has the greater speed at the instant of release? the ball thrown upward the ball thrown downward Neither; the speeds are the same.

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Part D

Which ball has the greater average speed during the 1-s interval after release (assuming neither hits the ground during that time)?

Which ball has the greater average speed during the 1-s interval after release (assuming neither hits the ground during that time)? the ball thrown upward the ball thrown downward Neither; the average speeds of both balls are the same.

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Part E

Which ball hits the ground with greater speed?

Which ball hits the ground with greater speed? the ball thrown upward the ball thrown downward Neither; the balls hit the ground with the same speed.

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Explanation / Answer

A)

a = g

The ball thrown up has a negative acceleration.

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B)

Neither; the accelerations of both balls are the same.

The ball thrown up is negative acceleration.

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C)

Neither; the speeds are the same

Both of the balls were given initial speed

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D)

the ball thrown downward

The ball thrown downward starts to speed up due to gravity. So speed is different for the two balls

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E)

Neither; the balls hit the ground with the same speed

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