Question

A 15kg. Blob of "space clay" moving at a speed of 3m/s slams I to a 12.5 blob of "space clay" at rest. They stick together after colliding, but what is their new speed?

What's the formula used and how do you solve this...?

Answer 1

Use the principle of conservation of momentum ... momentum after the collision is equal to the momentum before it.

Momentum = (mass) x (speed).

Momentum before the collision:
Big blob . . . (15) x (3) = 45 kg-m/s
Little blob . . (12.5) x (0) = zero.
Total . . . . . . 45 kg-m/s

Momentum after they meet and stick:
Combined blob . . . (15+12.5) x (speed)

Momentum after = momentum before:

(27.5) x speed = 45 kg-m/s

Divide each side by 27.5 :

Speed = 45 / 27.5  =  1.636 m/s  (rounded)