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On our test today the question said, "An 2 Kg object is moving along the x-axis and explodes, with particle 1, 1 Kg, shooting north at 3 m/s, and particle 2, 1 Kg, travelling 30 degrees north of east at 5 m/s. What was the initial velocity of the object?"

Now I was talking with a friend, and we each came up with two answers:

Would you treat it like an elastic collision, and if so, would you use the kinetic energy or momentum equations?

kinetic energy: ((m1v1i)^2)/2 + ((m2v2i)^2)/2 = ((m1v1f)^2)/2 + ((m2v2f)^2)/2

(2)(v1^2)/2 = (4.5) + (12.5)

v1 = 4.12

OR

m1v1i = m1v1f + m2v2f

2vi = 3 + 5

vi = 4

OR

Would you turn the problem into a triangle; since the velocity is 3 m/s going straight north, and 5 m/s 30 degrees north of east, you can turn it into a right triangle, and the missing side would have to be 4 m/s.

This question has been bugging me all day, until I finally decided to find this site, register, and ask you guys! haha. The answer of 4.00 m/s seems more reasonable, but it's weird that when you use the kinetic energy conservation equation that it ends up as 4.12 and not 4.00. Thank you in advance!

-Joe

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# Homework Help: Energy conservation question

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