# physics

posted by
**mandy**
.

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:

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.