A 1200 kg car is driving with a constant velocity of 25 m/s. What is the net force acting on the car?
Answers
Explanation:
Given info : A motorcar of mass 1200 kg is moving along a straight line with a uniform velocity of 90 km/h. Its velocity is slowed down to 18 km/h in 4 s by an unbalanced external force.
To find : the acceleration and change in linear momentum and also magnitude of force required.
solution : initial velocity, u = 90 km/h
= 90 × 5/18
= 25 m/s
final velocity, v = 18 km/h
= 18 × 5/18
= 5 m/s
we know, acceleration = change in velocity with respect to time.
so, acceleration, a = (final velocity - initial velocity)/time taken
= (5 - 25)/4
= -20/4
= -5 m/s²
change in linear momentum = final linear momentum - initial linear momentum
= mv - mu
= m(v - u)
= 1200 kg × (5 m/s - 25 m/s)
= 1200 kg × -20 m/s
= -24000 kgm/s
magnitude of force required, F = ma
= 1200 kg × 5 m/s² [ just taking magnitude of acceleration because we have to find magnitude of force ]
= 6000 N