1. Aug 8, 2007

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

A block of mass M = 3 kg is released from rest and slides down an incline that makes an angle q = 32° with the horizontal. The coefficient of kinetic friction between the block and the incline is µk = 0.15.

What is the acceleration of the block down the inclined plane?

2. Relevant equations
this is the easiste part of 4 part question and i cant get it.

3. The attempt at a solution
OK heres what i know
Normal = 3kg * (9.8sin32)
so friction is

fs = .15*15.58 = 2.34N
so i'm taking x axis as the incline plane, (pos x = down the plane)
friction opposes the motion, so force runs along neg axis = -2.34N

forces in pos x direction are
3 * 9.8cos32 = 24.93N

24.93N - 2.34N = 22.59N (this is the net force)

Finally F/m = a
22.69/3 = 7.53m/s/s

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

2. Relevant equations

3. The attempt at a solution

Last edited: Aug 8, 2007
2. Aug 8, 2007

### HallsofIvy

Staff Emeritus
Looks to me like you have sine and cosine reversed. You draw the inclined plane as a right triangle having angle 32 degrees at the bottom. The force of gravity is straight down, the two legs of that triangle are perpendicular and parallel to the inclined plane- the 32 degree angle is the bottom of that triangle. The normal force is given by cos(32), the force along the incline by sin(32).

3. Aug 8, 2007