. A 1.00 kg rock is thrown up into the air from ground level at a speed of 8.00 m/s. The ball travels up to a maximum height, then returns to the ground. Calculate the rock's momentum as it strikes the
ground.

p = -8 kg-m/s

Explanation:

Given that,

Initial speed of the rock, u = 8 m/s

Mass of the rock, m = 1 kg

The ball travels up  to a maximum height, then returns to the ground.

We need to find the rock's momentum as it strikes the  ground. Let v be the final speed of the rock. Its final speed is as same as initial speed i.e. 8 m/s but in negative direction. So

p = mv

p = 1 kg × (-8 m/s)

= -8 kg-m/s

So, the rock's momentum as it strikes the  ground is (-8 kg-m/s).

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.