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Selina Solutions Class 9 Physics Solutions for Exercise 2C in Chapter 2 - Chapter 2 Motion In One Dimension

Question 18 Exercise 2C

A car travels with a uniform velocity of 25m/s for 5s. The brakes are then applied and the car is uniformly retarded and comes to rest in further 10s. Find: (i) the distance which the car travels before the brakes are applied, (ii) the retardation and (iii) the distance travelled by car after applying the brakes.

Answer:

Given: u=25m/s; v=0;

(i) The distance which the car travels before brakes are applied is:

Distance = speed x time

= 25 x 5

= 125m

(ii) Retardation = (final velocity-initial velocity)/time taken

= -(5/2) = -2.5m/s2

(iii) To find distance travelled by the car after applying brakes

Time taken by the car to stop after applying brakes =10s

Assume ‘s’ to be the distance the car travels after brakes are applied

We know that v^2 - u^2 = 2as

(0 x 0) - (25 x 25)

= 2(-2.5)(s)

– 625 = -5s

s=125m

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