Question

a bike of mass 120 kg moving at a speed of 20m/s comes to rest in 40 sec due to frictional force alone calculate the friction force acting on the bike

Answer 1

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Answer 2

Given info : a bike of mass 120 kg moving at a speed 20 m/s comes to rest in 40 sec due to frictional force along it.

To find : frictional force acting on the bike.

Solution : frictional force opposes relative motion of body. So a force F acts just opposite to it due to which bike comes to rest.

Initial velocity of bike, u = 20 m/s

Final velocity of bike, v = 0

Time taken , t = 40 sec

Using formula,

V = u + at

⇒0 = 20 + 40a

⇒a = -0.5 m/s²

Now frictional force , F = ma

= 120 kg × -0.5 m/s²

= -60 N [ here negative sign indicates that frictional force acts just opposite the motion of bike. ]

Therefore magnitude of frictional force acting on the bike is 60 N