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**1. Homework Statement**

A Pendulum weighs .5kg and has a string length of 70cm swings from a horizontal position downwards to hit a block that weighs 2.5 kg and is on a frictionless plain. Calculate the speed of both the ball and the block after the elastic collision.

**2. Homework Equations**

mgh=.5mV^2

conservation of momentum

m1V= m1V1+m2V2

conservation of kinetic energy

.5m1V^2=.5m1V1^2+.5m2V2^2

**3. The Attempt at a Solution**

I used the first equation to solve for the initial velocity of the pendulum, which is 3.7m/s.

From here comes the elastic collision part.

I try to use both conseravation equations and substitute for one of the variables by solving for either V1 or V2 in either equation and thus substituting. However, when i try to solve it that way it ends up canceling out.

I know there is an equation for one dimension elastic collisions, but my professor says we can't use it unless we write the derivation of it, and that is a tedious thing to do and is rather lengthy.

Please help, ask questions if things are unclear