Object Slowing on a Horizontal Surface after Rolling down an Inclined Plane

[Caramon]

Homework Statement

Block A starts from rest and slides 8m down a frictionless 30 degree angled inclined plane. It then crosses a 4m horizontal surface where the coefficient of kinetic friction is 0.2. What is the velocity of Block A after it has finished crossing the horizontal surface?

(Note: It hits a ball at the end of a string after that and you have to find the height Ball B goes to, but I know how to do that If I can figure out the end velocity of Block A after it has crossed the horizontal surface).

Homework Equations

Kinematic Equations?
Fnet = ma?
Ff = uFn

The Attempt at a Solution

I am fairly sure that Block A is going 19.81m/s as it starts onto the horizontal surface but am not sure how to calculate the end velocity after crossing the frictional surface.

Thank you.

 

[nrqed]

Homework Statement

Block A starts from rest and slides 8m down a frictionless 30 degree angled inclined plane. It then crosses a 4m horizontal surface where the coefficient of kinetic friction is 0.2. What is the velocity of Block A after it has finished crossing the horizontal surface?

(Note: It hits a ball at the end of a string after that and you have to find the height Ball B goes to, but I know how to do that If I can figure out the end velocity of Block A after it has crossed the horizontal surface).

Homework Equations

Kinematic Equations?
Fnet = ma?
Ff = uFn

The Attempt at a Solution

I am fairly sure that Block A is going 19.81m/s as it starts onto the horizontal surface but am not sure how to calculate the end velocity after crossing the frictional surface.

Thank you.

There are two ways to do it: with the work-energy theorem or simply with F=ma and the kinematics equation of constant acceleration.

In that second way, you may use the two equations you wrote , $m a = - \mu F_N$. What is the normal force? That will allow you to find the acceleration. Then you may use the equations of constant acceleration, you know the distance, the initial velocity and the acceleration, you may find the final velocity.

Hope that helps

 

[Caramon]

Yeah, apparently I'm fking retarded. I forgot that Fnet = whatever the Ff is. I thought the object would be carrying some Fapp with it as it still had speed from coming down the inclined plane. I solved the problem.

Thanks for the help. :)