# Homework Help: The laws of motion - rock sliding on a roof

1. Dec 22, 2013

### haha1234

The laws of motion -- rock sliding on a roof

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

One side if the roof of a house slopes up at 37.0Â°.A roofer kicks a round,flat rock that has been thrown onto the roof by a neighborhood child.The rock slides straight up the incline with an initial speed of 15ms-1.The coefficient of kinetic friction between the rock and the roof is 0.400.The rock slides 10.0m up the rock and the roof crosses the ridge and goes into free fall, following a parabolic trajectory above the far side of the roof,with negligible air resistance.Determine the maximum height the rock reaches above the point where it was kicked.

2. Relevant equations

3. The attempt at a solution
Are there anything wrong?
Let the maximum height the rock reaches above the point where it was kicked be h.
1/2mv2=mgh+fs
1/2m(15)2=9.8mh+0.4xmx9.8xcos37Â°x10

Last edited: Dec 22, 2013
2. Dec 22, 2013

### Tanya Sharma

What is the acceleration the rock will undergo while sliding up the roof ? From this calculate the velocity of the rock just before it leaves the roof. What do you get ?

Edit :You can also approach this problem using Work Energy concepts .

Last edited: Dec 22, 2013
3. Dec 22, 2013

### SteamKing

Staff Emeritus
Angles are not measured in degrees Celsius.

4. Dec 22, 2013

### haruspex

That looks right to me.

5. Dec 22, 2013

### TSny

Does the rock have any kinetic energy when it reaches maximum height?

6. Dec 22, 2013

### haruspex

Do I still get to keep my award for the year?

7. Dec 22, 2013

### TSny

(Definitely!)

8. Dec 22, 2013

### haha1234

I think...no.
This is because all the energy will convert to potential energy.

9. Dec 22, 2013

### TSny

What would happen to the rock (which is traveling along a parabolic arc) if it came to rest at its highest point?

#### Attached Files:

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10. Dec 23, 2013

### haha1234

Thanks!I can find the correct answer now!

Last edited: Dec 23, 2013
11. Dec 23, 2013