Question 6
An unbalanced force of 8 N is applied for 3 s to a 2 kg trolley starting from rest. What is the trolley's momentum at the end of the 3 seconds?
The right answer is the one marked above.
24 kg m s−1. Three steps — force to acceleration, acceleration to velocity, velocity to momentum.
a = F ÷ m = 8 ÷ 2 = 4 m s−2
v = 0 + (4 × 3) = 12 m s−1
momentum = 2 kg × 12 m s−1 = 24 kg m s−1
The trolley starts from rest, so the initial velocity is 0 and the final velocity is simply a × t.
There is a short cut too: the force multiplied by the time equals the change in momentum — 8 N × 3 s = 24 kg m s−1. Same answer.