Question

A bus of mass 500 kg moving with a velocity of 20m/s is brought to rest by applying brakes if the frictional force is 1000N find the time taken

Answer 1

KE = loss in energy due to friction
1/2mv^2 = f x s
1/2 x 500 x 400 = 1000 x s
500 x 200/1000 = s
s = 100 m.

Answer 2

Given :  A bus of mass 500kg moving with a velocity of 20m/s is brought to rest by applying brakes if the frictional force is 1000 N.

To find: the time taken by the bus to come to rest.​

Solution:

frictional force is 1000 N.

F = -1000 N  as force is opposing the motion so negative sign

Bus mass = 500 kg

m = 500 kg

F = ma

=> -1000 = 500 ( a)

=> a = -2  m/s²

a = ( v - u)/t

v = 0  m/s as comes to rest

a = - 2 m/s²

u = 20  m/s  given

t = ?

=> - 2 = ( 0 - 20)/t

=> t = 10

Hence the time taken by the bus to come to rest.​ = 10 secs

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