(adsbygoogle = window.adsbygoogle || []).push({}); If the first ball in problem 7) has a mass of 10 kg and the second ball is travelling at it with a speed of 14 m/s, what is the velocity, to one decimal place, of the first ball after collision?

Problem (7) saysA 9.8 kg steel ball, travelling left to right at 12 m/s, undergoes an elastic collision with a 5 kg steel ball at rest. To the nearest Joule, what is the Total Kinetic Energy of the two balls after collision?

So I derived equations using the conservation of momentum and kinetic energy and I got the two formulas:

from Ek = Ek1+ Ek2

1) 980 = 10 v1(prime)^2 + 5 v2 (prime) ^2

-------------- ---------------

2 2

from m1v1 + m2v2 = m1v1 (prime) + m2v2 (prime)

2) 190 = 10v1(prime) + 5 (v2) (prime)

so then I divided them all by 5 and rearranged to solve for v2(prime) getting:

v2 (prime) = 2v1(prime) - 38

I substituted this eqn back into the first and got

980 = 10v1(prime)^2 + 5 (2v1(prime) - 38)^2

This rearranges into a quadratic eqn (i think) the after I solve for v1 prime I keep getting the wrong answer!!!! I'm not sure if it's just a math error or if I interpreted the question wrong... please help me!

thank you

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# Homework Help: Kinetic energy of balls after collision

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