# Using newtons law and mechanical energy?

1. Oct 26, 2013

### jimmyboykun

1. The problem statement, all variables and given/known data[/b]
A car is rolling down a ramp that is inclined at and angle of 9.9 degree with respect to horizontal. There is no friction acting from the road on the tires.

Employ conservation of mechanical energy to find the speed of a car that starts from rest and rolls down the ramp a distance of 52 m.

2. Relevant equations[/b]

1/2mv(initial)^2+mgh(initial)=1/2mv(final)^2+mgh(final)

3. The attempt at a solution[/b]
Vi=0m/s
Vf=?
hi=52m
hf=0

52mg=1/2vf

2*52m*9.81m/s^2=vf

√1020.24m^2s^2=√v

31.94m/s=v

I got a 1 out of ten in this problem. most likely got the units right, but my math did I used the right equation?

2. Oct 26, 2013

### subzero0137

The initial height is not 52 m. Draw a diagram to see why this is the case.

3. Oct 26, 2013

### jimmyboykun

ok I drew the free body diagram initial height is not 52m. would the 52 m be considered Δh?

4. Oct 26, 2013

### Tsunoyukami

Not quite - 52m is the distance the car travels down the ramp. It's change in height is not equal to this distance because this distance is composed of both the x and y distances. :)

5. Oct 26, 2013

### jimmyboykun

ok in this equation, where would the 52 m be placed, or am I using the proper equation for mechanical energy?

6. Oct 26, 2013

### subzero0137

No.
HINT: You have to use the value of the angle of the ramp and 52 m to get your Δh.