# Homework Help: Help! Kinetic Energy / Inclined Plane

1. Dec 16, 2008

### stonnn

1) A 1.0-kg object moving in a certain direction has a kinetic energy of 2.0 J. It hits a wall and comes
back with half its original speed. What is the kinetic energy of this object at this point?
Attempt at solution: 1/2mv^2 = 1/2m(0.5)v^2
2)
An object of mass 10.0 kg is released from the top of an inclined plane which makes an angle of inclination of 30.0 ° with
the horizontal. The object slides along the inclined plane. The questions refer to the instant when the object has traveled
through a distance of 2.00 m measured along the slope. The coefficient of kinetic friction between the mass and the
surface is 0.200. Use g = 10.0 m/s2.
How much work is done by the force of friction?

Attempt: mgh - mkmgd= 1/2mv^2
I keep getting the wrong answer for this one... is my equation wrong?

2. Dec 16, 2008

### LowlyPion

1 Careful with your parenthesis .... 1/2m(v/2)2

In 2. you need to draw a force diagram.

The normal weight to the incline is a function of the angle θ. It is the normal force*μ acting over that distance that will be the work done by friction

3. Dec 16, 2008

### Staff: Mentor

If the original kinetic energy = 1/2mv^2 = 2.0 J, what does the final kinetic energy equal? Hint: replace v with v/2.
Yes, your equation is a bit wrong. You didn't make use of the angle of inclination. How does the angle affect the normal force, and thus the friction force?

4. Dec 17, 2008

### stonnn

thanks for the hints, i'll work on them some more!