A constant retarding force of 50 N is applied to a body of mass 20 kg moving initially with a speed of 15 m s-1. How long does the body take to stop?
A. Given that, Force F=50N Mass m=20kg Initial velocity u=15m/s Now, from newton’s second law F=ma 50=20×a a=2.5m/s2 Now from equation of motion v=u+at 0=15+(−2.5)t t=2.515 t=6s Hence, the body will be stop in 6 sec. B. Given that, Mass of the body,m=3 kg Initial speed of the body u=2 m/s Final speed of the body v=3.5 m/s Time, t=25 sec Now, for acceleration Use the equation of motion v=u+at a=t(v−u) a=253.5−2 a=251.5 a=0.06 m/s2 Now, for the force Use the newton’s second law F=ma F=3×0.06 F=0.18 N The magnitude of the force is 0.18 N.
