A 2.5 kg stone is released from rest and falls toward Earth. After 4.0 s, magnitude of its momentum in kg. m/s is:

A-78

B-98

C-122.5

D-24.7

Answer:B

Explanation:

Initial velocity (u) = 0

Time (t) = 4seconds

Mass (m) = 2.5kg

acceleration due to gravity (g) = 9.8m/s^2

Final velocity (v) = u+gxt

Final velocity (v) = 0+9.8x4

Final velocity (v) = 39.2m/s

Momentum=mass x velocity

Momentum=2.5 x 39.2

Momentum=98kgm/s

B

Explanation:

momentum = mass * velocity

velocity = initial speed + acceleration * time where initial speed = 0, acceleration = 9.81, time = 4