Question

a car is moving with a speed of 20m/ s, all of a sudden a boy comes in way. The driver applies the brakes and car stops in

5 sec. calculate

a) retardation of car

b) distance travelled by car before it is stopped after applying the brakes.

Answer 1

Initial velocity, u = 20 m/s

Time taken to stop, t = 5 s

Final velocity, v = 0

Using, v = u + at

=> 0 = 20 + 5a
=> a = -4 m/s²

Negative sign indicates the car is slowing down. So, retardation is = 4 m/s²

Distance travelled by the car before stopping is,

S = ut + ½ at²

=> S = 20×5 – ½×4×5²

=> S = 100 – 50

=> S = 50 m