Question 7
An object of mass 3 kg is thrown vertically upwards. Its velocity as the motion begins is 10 m s−1. What is its momentum at launch, and at the maximum height it rises to?
The right answer is the one marked above.
30 kg m s−1 at launch; 0 at the top.
at launch: momentum = 3 kg × 10 m s−1 = 30 kg m s−1
At the maximum height the object's velocity is zero — we learned that in chapter 2. Since momentum = m × v:
at the top: 3 kg × 0 = 0
The mass has not changed, yet the momentum is zero. That is the point: momentum depends on velocity, so a stationary object always has zero momentum.