A 60 kg body is pushed with just enough force to start it moving across a floor and the same force continues to act afterwards. The coefficient of static friction and sliding friction are 0.5 and 0.4 respectively. The acceleration of the body is

Options

A. `6 ms^(-2)`
B. `4.9 ms^(-2)`
C. `3.92 ms^(-2)`
D. `1 ms^(-2)`

Answer

D

Explanation

When the body is just about to move, the force applied = Limiting friction
`= mu_sR`
= `mu_s mg`
` =0.5 xx 60 xx 10 = 300 N`
After the block starts moving, kinetic friction comes into play, Kinetic friction `=mu_kR`
`=mu_kmg`
`= 0.4 xx60 xx10 = 240 N`
As the coefficient of kinettic friction is less than that of the static friction, the body starts to accelerate.
Force applied on the body
= 300 N, net accelerating force
= Applied force - Kinetic friction
`implies ma = 300 – 240 = 60`
`:. a = 60/60 = 1 m//s^2`