Child X throws 0.5 kg of Play

Question

Dough at Child Y at 0.40 m/s at the same time that Child Y throws 0.8 kg of Play Dough at Child X at
0.20 m/s. The two masses of Play Dough collide and stick. What is the resulting speed and direction
of the Play Dough? What are the kinetic energies of the two masses before the collision? What is
the kinetic energy of the combined mass after the collision?

Answer 1

Since the masses stick together, there is conservation of momentum but no conservation of energy.

Let x be the new velocity.

Hence, 0.5*0.4 + 0.8*(-0.20) = (0.5+0.8)*x

X = (0.2-0.16)/1.3 = 0.0307 m/s

KE = 0.5*1.3*0.0307^2 = 0.000615 J.