# Kinematics - Short Question Solution | Physics Grade XI

### Short Question Answers

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#### Kinematics

Introduction to Kinematics

#### Viva Voice Questions # Kinematics - Short Question Answers

1. From a flying airplane, an object should be dropped in advance to hit the target. Why? When an object is dropped from the airplane, it travels in a parabolic path as in the figure. So, to exactly reach the target, it should be dropped in advance, else it won’t reach the target.

2. Is it possible to get a body accelerated even if it is moving with a uniform speed? Justify. (VVI)

Yes, it possible to get a body accelerated even if it is moving with a uniform speed if it is made to move in a circular path. In this case, even if the speed remains constant, direction velocity at each point changes and the acceleration is directed towards the center of the circle i.e. centripetal acceleration acts on the body.

3. A ball is dropped gently from the top of the tower and another ball is thrown horizontally at the same time. Which ball hit the ground first?

As we know, the time of flight of a projectile is given by T = √(2h/g), where ‘g’ is the acceleration due to gravity, it is independent of initial velocity or mass of the projectile. Since the balls are thrown from the same height, both hit the ground at the same time.

4. Can an object with constant acceleration reverse its direction of travel? Explain. (VVI)

Yes, an object with constant acceleration can reverse its direction of travel when it undergoes retardation i.e. if a body is moving towards north direction, due to retardation constant acceleration is directed just opposite south direction.

5. Give with an example a case where the velocity of an object is zero but its acceleration is not zero.

When an object is thrown up, then at the highest point, the body comes to rest for a fraction of second where its velocity becomes zero but acceleration doesn’t become zero due to gravity i.e. its acceleration is equal to acceleration due to gravity.

6. Can you have zero acceleration but non-zero velocity? Explain with the help of a graph. Yes, we can have zero acceleration but non-zero velocity when a body is moving in a uniform motion. Here in the figure, OP has a uniform acceleration and increasing velocity whereas PQ has constant velocity and acceleration is zero. 8. A swimmer wants to reach to a point just opposite on the other bank of the river. How should he swim and why? Let us consider the river is flowing with velocity v, as shown in the figure. A swimmer wants to reach point B just opposite on the other side of the bank of the river from point A. Then he has to move with the direction making an angle θ with the AB as shown in the figure. From the figure, θ = tan-1(Vr/VR).

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