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Notaphysicsmajor
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Homework Statement
A 10kg block moving at 1 m/s hits another 10kg stationary block. Those two blocks (now stuck together) collide with another 10kg stationary block. What percent of the original energy is lost after the two collisions?
Homework Equations
m1v1 + m2v2 = (m1+m2)v3
Kinetic energy = .5(m)(v)^2
The Attempt at a Solution
Hello,
I'm not sure if I understand this problem correct so I hope someone here can help me, but here is how I solved it.
First collision:
(10)(1) + (10)(0) = (20)v
Velocity = .5 m/s
Second collision:
(20)(.5) + (10)(0) = (30)v
Velocity = .3
Initial energy (before any collision):
.5(10)(1)^2 = 5 J
Energy after first collision:
.5(20)(.5)^2 = 2.5 J
Energy after second collision:
.5(30)(.3)^2 = 1.6 J
1.6 J is amount of kinetic energy after both collisions, but problem asks what percent of the original energy was lost after first two collisions.
So 5 - 1.6 = 3.4 J energy lost after first two collisions.
3.4 / 5 = .68 or 68%. 68% of original energy was lost after first two collisions.
Is this correct?