Question

A motorcar of mass 1200kg is moving along a straight line with a uniform velocity of 90km/h . Its velocity is slowed down to 18km/h in 4s by unbalanced external force . calcullate the acceleration and change in momentum and also the magnitude of force.

Answer 1

nitial velocity = 90km/h = 90 ×5/18 m/s = 25m/s   final velocity = 18 km/h = 18× 5/18 m/s = 5 m/s  acceleration = (final velocity -initial velocity )/ time taken                       =( 25 - 5)/4 = 5 m/s²now, change in momentum = m( final velocity - initial velocity )                                       =1200 ×( 25 - 5) = 24000 Kgm/s 
force = change in momentum / time           = 24000/4 = 6000 N