A 120 kg mass is blown apart into an 80 kg piece and 40 kg piece. after the blast, the two masses are moving apart with a relative velocity of 60 m/s. the total kinetic energy after the explosion is:

Question

A. 21 kJ
B. 35 kJ
C. 48 kJ
D. 56 kJ
E. 82 kJ

Because of momentum conservation rules, the two pieces must go in opposite directions with
V2 = 2 V1
V1 is the final speed of the 80 kg piece; V2 is the final speed of the 40 kg piece.
Furthermore, because of the relative velocity that was given,and the opposite directions of motion,
V1 + V2 = 60 m/s
V1 + 2V1 = 60
V1 = 20 and V2 = 40 m/s
Now compute KE = (M1/2) V1^2 + (M2/2) V2^2
and see which answer is correct.

Answer 1

48000