# Homework Help: Work and energy

1. Mar 17, 2005

### kinski_girl

K. if anyone is able to help me with this problem, that would be great.

A student carries a 1.0 kg physics book 3.0 m across the room, then lifts it 1.5 m to put it on a shelf. The entire task takes 20 s.
a) what is the total work done on the book?
b) what is the change in potential energy of the book?
c) what is the power output of the student?
d) if the book falls off the shelf a distance of 2.5 m to the floor, how much kinetic energy will it have when it hits the floor?
e) what is the speed of the book as it hits the floor?

2. Mar 17, 2005

### marlon

Well you know that the potential energy associated with gravity is mgh where h is the vertical distance that anobject is rised.

The work is equal to F*r*cos(x) where F is the force, r the travelled distance and x is the angle between the force vector and the travelled distance. If both F and r are parallel then the work is just F*r...

The power is the work F per unit of time : F/t...

This should get you going

marlon