Which car is harder to stop and why?
calculate the momentum of cars a and b, and then
answer the question
car a:
mass: 1,000 kilograms
velocity: 40 meters/second
car b:
mass: 4,000 kilograms
velocity: 10 meters/second

The momentum of bath cars is 40000 Ns which make the difficulty to stop each car in aspect of fprce is the same.

Explanation:

Momentum (P) =mass(m) × velocity (v)

For car A,

                    P = m × v = 1000 × 40 = 40000 Ns

For car B,

                    P = m × v = 4000 × 10 = 40000 Ns

Force (F) = Momentum change(ΔΡ)/ time taken(t)

            F = ΔΡ/t

When stopping the car the momentum changes from 40000 Ns to 0

So momentum change in both cars is the same. So to stop the two cars in a  given time (t) you need the same force, which means you will feel same difficulty.

be subject to a force andchange its motion