Kinetic energy of a ball rolling down a ramp

[kaloyan]

Homework Statement

Consider the situation in the attached photo. The kinetic energy in A is 10 J, in B is 30 J. What is the kinetic energy in C?

Relevant Equations

no equations

Consider the situation in the attached photo. The kinetic energy in A is 10 J, in B is 30 J. What is the kinetic energy in C?

Using that the mechanical energy is the sum of potential energy $(E_p=mgh)$ and kinetic energy $(E_k=\dfrac{mv^2}{2})$, we get that the mechanical energies in $A,B,C$ are $E_A,E_B,E_C$, respectively: $$E_A=10J + mg(3h+h_2)$$ $$E_B=30J + mg(h+h_2)$$ $$E_C=E_{k_c}+mgh_2$$ They must be equal. In other words: $$10J + mg(3h+h_2)=30J + mg(h+h_2)=E_{k_c}+mgh_2$$

 

[Gaussian97]

Please, post your try, then we will know how to help you.

 

[haruspex]

Homework Statement:: Consider the situation in the attached photo. The kinetic energy in A is 10 J, in B is 30 J. What is the kinetic energy in C?
Homework Equations:: no equations

Consider the situation in the attached photo. The kinetic energy in A is 10 J, in B is 30 J. What is the kinetic energy in C? View attachment 255522
Using that the mechanical energy is the sum of potential energy $(E_p=mgh)$ and kinetic energy $(E_k=\dfrac{mv^2}{2})$, we get that the mechanical energies in $A,B,C$ are $E_A,E_B,E_C$, respectively: $$E_A=10J + mg(3h+h_2)$$ $$E_B=30J + mg(h+h_2)$$ $$E_C=E_{k_c}+mgh_2$$ They must be equal. In other words: $$10J + mg(3h+h_2)=30J + mg(h+h_2)=E_{k_c}+mgh_2$$

Good so far. You have a system of equations and unknowns. You only care about finding one of the unknowns. So what do you do next?

 

[Gaussian97]

Maybe will help you to think about what is the potential energy, and remember that doesn't make sense to talk about absolute potential energy, only its difference is measurable.