Q. 84.4( 5 Votes )

# Give Reasons for the Following:

Can a body move with constant acceleration but with zero velocity? If yes, why?

Answer :

Acceleration is the rate of change of velocity. In order to have non-zero acceleration, rate of change of velocity should be non-zero.

Yes, it is possible to have non-zero acceleration at zero velocity. But it is only possible for a moment. A moment is a brief period that cannot be measured.

Let us understand it by following two examples:

a) When we throw a ball in the air, it attains a maximum height and then comes down. At the maximum height velocity of the ball is zero, but a negative acceleration due to gravitation acts on it.

b) When we apply brakes on a moving car, the car stops and the velocity of the car is zero at that moment but acceleration (retardation) is not zero.

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Given figures represent the motion of two objects P and Q. Which of the objects has positive acceleration and which one has negative acceleration?

Fill in the blanks.

(i) ………..is the term used for negative acceleration.

(ii) A bus starting from rest attains a velocity of 54 km/h in 60 s, its acceleration is …………….. .

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