Question

A motor car of mass 1200kg is moving along a straight line with a uniform velocity of 90km/h.itsmvelocity is slowed down to 18km/h in 4 s by an unbalanced external force.calculate th acceleration and change in momentum of the car . Also calculate the magnitude of force required.

Answer 1

Here, m = 1200 kg, m = 90 km/h = 90*1000 m60*60 s25 m's

v = 18 km/h = 18*1000 m60*60 s= 5m/s,t = 4s

Alcceleration,a =v-ut = 5-254=5 m/s^2

Change in momentum = m (v - u) = 1200 (5 -25) = -24000 kg m's

Force required, F = ma = 1200 (-5) = -6000 N

Magnitude of force required = 6000 N

Negative sign shows that force is opposing the motion.

Answer 2

Acceleration =V2 _ v1 / t =5m/s2
F=ma =12oo×5 =6000
F= rate of change of momentum
F= momentum /time
Momentum =6000× 4= 24000