Question

13.) A car travels with a uniform velocity of 25 m si for
5 s. The brakes are then applied and the car is
uniformly retarded and comes to rest in further
10 s. Find : (i) the distance which the car travels
before the brakes are applied, (ii) the retardation,
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Answer 1

(i) distance = velocity × time

= 25 m/s × 5 s

= 125 m

(ii) retardation = final vel - initial vel / time

= 0 - 25 / 10 [Since car become rest on applying brakes, so final vel = 0]

= -5 / 2

= -2.5 m/s^2

Answer 2

i). uniform velocity of car, u = 25 m/s

car travels with uniform velocity of 25 m/s for 5 sec.

so, distance travelled by car before the brakes are applied = vt = 25 × 5 = 125m

ii) final velocity of car , v = 0

time taken by car to become rest , t = 10s

now using formula,

v = u + at

0 = 25 + a × 10

or, a = -2.5 m/s² , here negative sign indicates a is retardation.

hence, retardation is 2.5 m/s²