# MCQ helpWatch

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Thread starter 12 years ago
#1
A boy throws a ball vertically upwards. It rises to maximum height, where it is momentarily at rest, and falls back to his hands.

Which of the following gives the acceleration of the ball at various stages in its motion? Take vertically upwards as positive. Neglect air resistance.

A. rising -g , at maximum height 0, falling +g
B. rising -g , at maximum height -g, falling -g
C. rising g, at maximum height g, falling g
D. rising g, at maximum height 0 , falling -g

The answer was given B. Why??
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12 years ago
#2
Acceleration = Deceleration in physical terms.

Imagine a velocity-time graph, the graph will slope downwards until from when the ball is released until it hits his hand again, thus a negative acceleration.

The ball is always accelerating downwards, because its under gravity.
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12 years ago
#3
Gravitational force is always down so the acceleration is always down.
Up is defined as positive in the question so the acceleration must always be negative.
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12 years ago
#4
the acceleration of the ball is constant and equal to g downwards. The velocity of the ball may go from negative to zero to positive (if positive is downwards)

What a c rap question.
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3 years ago
#5
Acceleration is always constant, which is g.
When it moves upward, the velocity decrease to zero which then means deceleration thus -9.81..
When it falls down, itll be negative since th question said take vertically upwards as positive(even when the velocity increase) *if u understand my explaination
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