Laws of conservation of mass (roller coaster) work and mechanical energy

[anna sung]

Homework Statement

A 4.0 x 10^4kg roller coaster starts from rest at point A. Neglecting Friction, calculate its potential eneregy relative to the ground, its kinetic energy, and it's speed at points, B, C, and D.
at point A : 54m
B: 15m
c:47m
d:35m

Homework Equations

i got potential eneregy by using Eg=mgh
but how do you get the kinetic eneregy when you don't have velocity.
also when writing down equations what do you write after
L.C.E. is it due to L.C.E. Ek=Eg?

 

[PhanthomJay]

Homework Statement

A 4.0 x 10^4kg roller coaster starts from rest at point A. Neglecting Friction, calculate its potential eneregy relative to the ground, its kinetic energy, and it's speed at points, B, C, and D.
at point A : 54m
B: 15m
c:47m
d:35m

Homework Equations

i got potential eneregy by using Eg=mgh
but how do you get the kinetic eneregy when you don't have velocity.
also when writing down equations what do you write after
L.C.E. is it due to L.C.E. Ek=Eg?

The law of conservation of energy when only conservative forces like gravity are doing work states that the change in Ek plus the change in Eg = 0, that is $$\Delta E_k + \Delta E_g = 0$$, or putting it in another form,
$$E_k_{initial} + E_g_{initial} = E_k_{final} + E_g_{final}$$. Using either one of those equations should be very helpful in calculating the coaster's kinetic energy at a given point.

 

[anna sung]

yes. that is what i did. i posted another one. could you please have a look at it and tell me what i am doing wrong.
https://www.physicsforums.com/showthread.php?p=2969343#post2969343