How Does Friction Impact Block Velocity in a Multi-Height Path?

[dominus96]

Kinetic Energy with diagram!

Homework Statement

In the figure below, a small block is sent through point A with a speed of 7.5 m/s. Its path is without friction until it reaches the section of length L = 12 m, where the coefficient of kinetic friction is 0.70. The indicated heights are h1 = 6.5 m and h2 = 1.6 m.

(a) What is the speed of the block at point B?
(b) What is the speed of the block at point C?

Homework Equations

K=.5(mv^2)
U=mgh
F=ma
Friction force=mu*force normal

The Attempt at a Solution

First off, ignore the friction stuff because I already got those. I just need help with the 2 specific questions I listed. For a I did K=U so I set .5v^2=gh since the masses cancel out. But I got velocity and it was wrong...

 

[bullardz]

Ooo! I did this one a while back.

Ok the reason you missed the first one is because U @ point a does NOT equal K @ point B. U+K @ a does though. Don't forget it's initially moving.

 

[dominus96]

So U+K(point A)=K(point B)?

 

[shawshank]

what's point d in there for then, lol

 

[dominus96]

It's for another part of the problem I already figured out so don't worry about it lol.

 

[shawshank]

cooolio

 

[bullardz]

indeed. the second question is similar. Energy total @ point b = energy total @ c

Ergo... K(@b)=U+K(@c)

 

[dominus96]

Thanks!

 

[bullardz]

Sure