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April 21, 2014

Homework Help: physics

Posted by mandy on Monday, August 6, 2007 at 12:05am.

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.

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