A block is projected with speed 20 m/s on a rough horizontal surface. The coefficient of friction (u) between the surfaces varies with time (t) as shown in figure. The speed of body at the end of 4 second will be ( g = 10 ms-2 ) :- a) 2 m/s b) 5 m/s c) 7.2 m/s d) 9.5 m/s Share with your friends Share 54 Ved Prakash Lakhera answered this The motion is taking place under the action of balanced forces.So the force which moves the blockis, m a = μ mgor a = μ gor a = 0.5×10=5m/s2where a is the retardation on the block due to friction.since this retardation is acting continously for 2second, so now according to eqn of motion, v = u-at=20-5×2=20-10=10m/s again retardation due to decrease in co efficient of friction between time 2 second to 4 second is given by, a' = μ'×g=.22×10=1 since friction is varying with time, so μ'=dv/dt =.5-.32or μ' =.2/2again applying eqn of motion, v' = v-a't=10-1×2=8m/s.Therefore final velocity is 8m/s.So non of the options are correct. -160 View Full Answer Vasav answered this Answer plzz..... -33
