Question

An object is thrown upward with an initial velocity of 32.1 m/s. When the object reaches it maximum height, it is true of the acceleration, a, and the velocity, v, that:

both its acceleration and velocity are zero

both its acceleration and velocity change sign

velocity is equal to zero, but acceleration is not

acceleration is equal to zero, but velocity is not

None of the above.

Please help. Only one answer is true. Please give reason why.

Answer 1

ANSWER: Option 3: Velocity is equal to zero, but acceleration is not.

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Given that the object is thrown upwards, so there is no horizontal velocity only vertical velocity.

Vertical velocity changes because there is acceleration in vertical direction which is the acceleration due to gravity,

Acceleration due to gravity cannot be zero and it is always present (In this case). So we can ignore options 1 and option 4

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Acceleration due to gravity is always acting downwards and it does not change sign.

So ignore option 2.

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Initially, the upward velocity is 32.1m/s. As the object rises, its velocity decreases due to g.

The object will reach a certain height where the vertical velocity becomes zero. That height is the maximum height.

So correct answer is Option 3

After that, the object starts falling and accelerating downwards.

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Since only one answer is true and we already got the correct answer. Option 5 is wrong.

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