Question

Dear sir,

Please help me with the question below.

A car moving with speed of 54 km/h is brought to rest within 10 sec by applying break. Find the acceleration due to breaks.

Answer 1

Given Initial Speed (u)= 54 km /hr = 54 *1000 m / 3600 s = 54*5/18 = 15 m/s

( 1km = 1000 m and 1hr = 60 mins = 60*60 seconds = 3600 seconds)

Time t = 10 seconds

Final Velocity (v) = 0 Finally cat is at rest.

we know that ,

v = u + at

0 = 15 + a*10

0 = 15 + 10a

a = -15/10m/s² = -1.5 m/s²

Therefore , acceleration is -1.5 m/s²

Negative sign indicate that the acceleration is directed against the motion of car ,so retardation is 1.5 m/s².