# NCERT Physics Class 11 Exemplar Ch 4 Motion in A Plane Part 3

## VSA

16 A cyclist starts from centre O of a circular park of radius 1km and moves along the path OPRQO as shown. If he maintains constant speed of, what is his acceleration at point R in magnitude and direction?

Ans: 16.

in the direction RO.

17 A particle is projected in air at some angle to the horizontal, moves along parabola as shown in Fig. 4, where x and y indicate horizontal and vertical directions, respectively. Show in the diagram, direction of velocity and acceleration at points A, B and C.

Ans:

The students may discuss with their teachers and find answer.

18 A ball is thrown from a roof top at an angle of above the horizontal. It hits the ground a few seconds later. At what point during its motion, does the ball have

(a) Greatest speed.

(b) Smallest speed.

(c) Greatest acceleration? Explain

Ans:

(a) Just before it hits the ground.

(b) At the highest point reached.

(c) constant.

19 A football is kicked into the air vertically upwards. What is its (a) acceleration, and (b) velocity at the highest point?

Ans:

• Acceleration.

• Velocity.

20 A, B and C are three non-collinear, non-co-planar vectors. What can you say about direction of?

Ans:

Since is perpendicular to plane of B and C, cross product of any vector will lie in the plane of B and C.

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