# Where brick hits ground after sliding off a roof w/ friction

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1. Dec 19, 2015

### isabelrose

1. The problem statement, all variables and given/known data
Brick is sliding off a roof, starts at the peak of the roof (7.0 m above ground), slides down roof with kinetic friction value of 0.28, very edge of roof is 4.0 m above ground. Where does the brick land on the ground?

2. Relevant equations

3. The attempt at a solution
I attempted the solution by:

drawing force diagram of brick (@ = angle of incline, 30 degrees) which gives the acceleration down (acceleration down the roof = positive direction) the roof by:
ma = mgsin@ - frictional force
ma = mgsin30 - 0.28

Now should I just continue to solve for the acceleration and then treat this as a projectile? If so, can someone walk me through it?

Thanks!

2. Dec 19, 2015

### haruspex

0.28 is not the frictional force. It is the coefficient of kinetic friction. How do you obtain the frictional force from the coefficient?

3. Dec 20, 2015

### isabelrose

Oh yeah!
The frictional force (Ff) = coefficient of kinetic friciton * Fn = 0.28 * mgcos@

4. Dec 20, 2015

### haruspex

Good.
So, at what speed does it leave the roof?