Question

A car of mass 1200kg changes its velocity from 90km per hour to 18km per hour in 4secs due to an external force. Calculate,.1.Acceleration, 2.Change in momentum, 3.External force

Answer 1

Converting speeds into m/s
18km/h = 18×5/18=5m/s
90km/h = 90×5/18=25m/s

acceleration=(v-u)/t

a= (5-25)/4
a=-20/4
$a = - 5m s {}^{ - 2}$
Change in momentum = mu-mv
=m(v-u)
=1200(5-25)
=1200(-20)
=-24000m^2/s

Force = rate of change of momentum
=-24000/4
=-6000N