A roller-coaster car with a mass of 850 kg starts at rest from a point 24 m above the ground. At point B, it is 12 m above the ground.
(a) What is the initial potential energy of the car?
(b) What is the potential energy at point B?
(c) If the initial kinetic energy was zero and the work done against friction between the starting point and point B is 30 000 J, what is the kinetic energy of the car at point B?

I thought you used the equation PE=mgh, but I am getting all of my answers marked wrong

Question

A roller-coaster car with a mass of 850 kg starts at rest from a point 24 m above the ground. At point B, it is 12 m above the ground.
(a) What is the initial potential energy of the car? 
(b) What is the potential energy at point B? 
(c) If the initial kinetic energy was zero and the work done against friction between the starting point and point B is 30 000 J, what is the kinetic energy of the car at point B? 

I thought you used the equation PE=mgh, but I am getting all of my answers marked wrong

anonymous · Answer

I believe you'll find the following expressions useful here:

Potential Energy:$$E_{p}=mgh$$
Kinetic Energy:$$E_{k}=\frac{1}{2}mv^{2}$$

Assume that these quantities are conserved; that is the quantity is Etotal is conserved:$$E_{total}=E_{p}+E_{k}$$

anonymous · Answer

Wouldn't I just have to use the PE=mgh formula for parts A and B though? Since it's asking for the potential energy?

anonymous · Answer

I'm confused