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A ball of mass 4 kg is moving with a speed of 10 m/s. Its speed reduces to 5 m/s due to frictional force. The work done by frictional force is (1) 150J(2)-150J(3) 75J(4) -75J |
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Answer» 2.-150 JExplanation:Given:m=4 kgu=10 m/sv=5 m/sSolution:VARIOUS forces ACTING on the body are:Normal reaction in vertically upward directionweight of the body in vertically downward directionForce of friction in the opposite DIRECTION of motionThe change in velocity is only due to frictional force cause WEIGHT and normal reaction are balanced and contribute nothing in changing the velocity as they are acting in a different plane.mg=N (in vertical direction)From work energy theorem we know thatWork done by all the forces=change in kinetic energyW=ΔKE=KEf - KEiKEf=1/mv²=1/2*4*5²=50 JKEi=1/2mu²=1/2*4*10²=200 JthereforeW=50-200=-150 JHence frictional force does -150 J of work.PS: the NEGATIVE sign indicates that force and displacement are in opposite direction.Hope this helps |
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