Question

A ball is thrown vertically upwards. The positive direction is taken to be in upward direction.Which of the following is the correct sign of the quantities during its ascent?

| POSITION| VELOCITY| ACCELERATION
---|---|---|---
A| Positive| Positive| Positive
B| Positive| Positive| Negative
C| Positive| Negative| Negative
D| Negative| Positive| Negative
E| Negative| Negative| Negative

Answer 1

Every object when thrown on the earth surface, it returns back to the earth due to its force of gravitation on the surface. The earth surface is considered as the zero level and the value increases as it goes upward either it can be position or the velocity. Gravity acts downward.

Complete answer:
When the body is thrown upwards, it moves up until the velocity of the ball becomes zero and the force exerted on it becomes zero. After that the ball reaches the ground with the acceleration due to gravity with the zero velocity. When the ball goes up, the height of the ball increases and it also moves up. Thus the position becomes positive. The ball goes up with some velocity obtained by the force exerted by the person who throws the ball. This is limited up to the ball force of the ball is zero.
Though the velocity of the ball when moving up decreases, the direction is upward. Hence the velocity of the ball is also positive. The acceleration that acts on the body is due to the gravitational force. The acceleration due to gravity is downwards towards the surface of the earth. Hence in this case the downward is considered as positive and the upward is considered as negative. Since the acceleration moves the ball up against the force of gravity, it is negative.

Thus the option (A) is correct.

Note:
Let us consider one example of this case. When the rocket is launched, it goes up using the fuel in it. The force is provided by the fuel to move up until it overcomes the earth gravitational force. This velocity of the rocket is called by the name escaping velocity.