# Mometum and Energy

clarkandlarry

## Homework Statement

A 64kg student is standing in the middle of a frozen pond with a frictionless surface while carrying 2 books, a physics book with a mass of 2.5kg and a biology textbook with a mass of 3.5kg. The physics book is thrown with a speed of 6m/s relative to the student to the right and then the biology book is thrown in the opposite direction with a speed of 4m/s relative to the student. Calculate the velocity of the student after the biology book is thrown.

## Homework Equations

Not entirely sure
E = 1/2mv(squared)??

## The Attempt at a Solution

I don't have a clue how to start this question. Please any help would be greatly appreciated.

CrazyIvan
There are 3 objects under consideration: The student, the physics book, and the biology book.

Start by considering the law of conservation of momentum. What is the combined momentum of all three before and after the collision? What is the momentum of each individual object before and after the collision? How are these related?

clarkandlarry
Would the combined momentum be 0 before and after the collision?

CrazyIvan
Yes.

clarkandlarry
but how would i calculate the velocity of the person after he throws each textbook? i don't understand what equation (s) i would use.