1.

A bullet of mass 20 g leaves a riffle at an initialspeed 100 m/s and strikes a target at the samelevel with speed 50 m/s. The amount of work doneby the resistance of air will be(1) 100 J(3) 75 J(2) 25 J(4) 50 J

Answer»

by work - energy theorem,initial KE - final KE = work performed against air resistanceInitial KE = 1/2 * m * vi^2(i- initial)Final KE = 1/2 * m * vf^2(f- final)Hence change = 1/2 * 20/1000 * (100^2 - 50^2) = 1/100 * 150 * 50 =75 JSo work done by bulllet against air resistance = 75 JOr work performed by air to reduce the energy of bullet =75 J



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