An 11-kg ball moving at 15 m/s collides elastically and head-on with a second 5-

Question

An 11-kg ball moving at 15 m/s collides elastically and head-on with a second 5-kg ball moving in the opposite direction with -4 m/s. What is the speed of the first ball after the collision? Give your answer in m/s to three significant figures.

Explanation / Answer

here, the collision is head-on and elastic. therefore, we will use the conservation of momentum. m1.u1+m2.u2=m1.v1+m2.v2----------------------1 and the second equation, we will use for e. e=1 (for elastic collisions) e=(v2-v1)/(u1-u2)------------------------------2 now from 1-> 11*(15)+5(-4)=11(v1)+5(v2) 145=11(v1)+5(v2)--------------------------A and from 2-> 1=(v2-v1)/15-(-4) v1-v2=-19--------------------------------------B solving A and B simultaneously, v1= 3.125 m/s v2= 22.125 m/s the speed of the first ball after the collision= 3.125 m/s

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