A15kg. 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

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)

Iwould sure like to answer your question but i honestly just don’t know