A 20-kg object sitting at rest is struck elastically in a head-on collision with a 10-kg object initially moving at 3.0 m/s. Find the final velocity

1 m/s

Explanation:

Using law of conservation of momentum

m1v1 + m2v2 = (m1 + m2)vf , where

m1 = mass of object at rest, 20 kg

v1 = initial velocity of object at rest, 0 m/s

vf = final velocity of the bodies

m2 = mass of object in motion, 10 kg

v2 = initial velocity of object in motion, 3 m/s

On substituting, we have

(20 * 0) + (10 * 3) = (20 + 10) vf

0 + 30 = 30 vf

vf = 30 / 30

vf = 1 m/s

Therefore, the velocity of the bodies after hitting each other is 1 m/s

real, smaller and upside-down.   so the answer should be b.