A block of mass 15 kg is placed on a long trolly . The coefficient of friction between the block and trolly is 0.18 The trolly accelerates from rest at ` 0.5 m//s^(2) ` for 20 seconds and then moves with a unifrom velocity Discuss the motion of the block as viewed by (i) a stationary observer on the ground (ii) an observer moving with the trolly .

Explanation

Here , `m = 15 kg , mu = 0.18`
`a = 0.5 m//s^(2) t = 20 s`
Force on the block due to motion of trolly
`F= ma = 15 xx 0.5 = 7 .5 N`
This force is in the direction of motion of trolly force of limiting friction on the block
` F = mu R = mu mg = 0. 18 xx 15 xx 9.8 = 26.46 N`
It opposes the motion of the block As `F lt F` therefore the block will not move The force of state friction (F) will adjust itself equal and opposite to the applied force Hence to a stationary observer on the ground the block will appear to be at rest relative to the trolly . When trolly moves with unifrom velocity the block will continue to be stationary Because in that case forward force is zero and force of friction alone is acting on the block . (ii) An observer moving with the trolly has accelerated motion Hence the observer is non inertial The law of inertia in no longer valid