A 1000 kg car starts from rest and reaches 30 m/s in 5 s. What average force is required?

A 1000 kg car starts from rest and reaches 30 m/s in 5 s. What average force is required?

• A. 600 N
• B. 2000 N
• C. 6000 N
• D. 30 N

Answer: (C)

This question tests how average force relates to acceleration and momentum. The car has mass 1000 kg, starts from rest and reaches 30 m/s in 5 s, so its average acceleration is a = (v − u)/t = (30 − 0)/5 = 6 m/s^2. Using F = m a, the average force is F = 1000 kg × 6 m/s^2 = 6000 N. You can also see this through momentum change. The car’s momentum changes by Δp = mΔv = 1000 kg × 30 m/s = 30000 kg·m/s. The average force over the 5 s interval is F_avg = Δp/Δt = 30000 / 5 = 6000 N. So the required average force is 6000 newtons.

This question tests how average force relates to acceleration and momentum. The car has mass 1000 kg, starts from rest and reaches 30 m/s in 5 s, so its average acceleration is a = (v − u)/t = (30 − 0)/5 = 6 m/s^2. Using F = m a, the average force is F = 1000 kg × 6 m/s^2 = 6000 N.

You can also see this through momentum change. The car’s momentum changes by Δp = mΔv = 1000 kg × 30 m/s = 30000 kg·m/s. The average force over the 5 s interval is F_avg = Δp/Δt = 30000 / 5 = 6000 N. So the required average force is 6000 newtons.