(wasn't sure if I should post this in the general physics or in the "homework" forum.... this question is loosely based on a problem found in a printed book, but I have modified it myself.... regardless, here is the situation)(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

A person is sliding down a frictionless incline.

The person started at rest at an initial height ofimeters above the ground, and has slid down some distance (so their vertical elevation is now only 3/5*i, or some such).

At this point the person throws a block that s/he is carrying in exactly the opposite direction to their velocity.

2. Relevant equations

conservation of momentum, conservation of mechanical energy

3. The attempt at a solution

Momentum is conserved, and assuming that there are no losses of energy, energy should be conserved too.

But, for some reason when I try to solve the equations, I only receive complex solutions. I am stumped.

I am pasting the equations that I used below:

(values/variables:

3kg is the mass of the block thrown away

20kg is the mass of the block and person

15m is the initial height

12m is the height above ground at which the block is thrown away

c is the magnitude of the velocity of the block

f is the magnitude of the velocity of the person after the block is thrown away

n is the total mechanical energy of the system

Total mechanical energy after the block is thrown away

1/2*3*c^2+20*9.8*12+1/2*(20-3)*f^2=n

Total mechanical energy at the top of the incline

20*9.8*15=n

Conservation of momentum

20*v=(20-3)*f-c*3

The magnitude of the velocity of the block-and-human immediately before the block is thrown away

v^2=2*9.8*15

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# Homework Help: Conservation of momentum and mechanical energy

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