Question

A car travels with the uniform velocity of 25 m/s for five seconds. The brakes are then applied and the car is uniformly retarded and comes to rest in further 10 seconds. Find:
1)The distance which the car travelled before the brakes are applied
2)The retardation
3)The distance travelled after the brakes are applied.

Answer 1

Given:
1) u = 25m/sec
Distance it travels in 5 sec
Distance travelled before the brakes are applied = $25\times 5$ = $125m$

2) After 5 sec brakes are applied
It then comes to rest in 10 sec
u = 25 m/s
v = 0 (as it comes to rest)
t = 10
a = change in velocity/time = -25/10 = -2.5 $m/s^2$

3)
$s=ut+\frac{a{t}^2}{2}$
$s=25\ast 10+\frac{-2.5\ast 100}{2}$ = 250 - 125 = 125 m

Hence, the distance it travels after the brakes are applied is 125m