Deceleration of rocks sliding up a hill

[jamiebean]

Homework Statement

attached below

Relevant Equations

kinetic coefficient x normal force= kinetic energy

i have no idea how did the answer come in conclusion...i guess that cosθ and sinθ is referring to the 2 dimensions of the acceleration ? but how? and why?

 

[berkeman]

Homework Statement:: attached below
Relevant Equations:: kinetic coefficient x normal force= kinetic energy

i guess that cosθ and sinθ is referring to the 2 dimensions of the acceleration ?

Yes. Do as they suggest and draw a FBD. That will help you to resolve the components.

BTW, I think the answer given is wrong -- it has a sign error, no?

 

[kuruman]

There are two terms to the acceleration because there are two separate forces opposing its uphill motion. What are these two forces?

Edit: Rats! @berkeman beat me to it.

 

[berkeman]

BTW, I think the answer given is wrong -- it has a sign error, no?

Unless by "base" they mean the top of the hill? That would usually be referred to as the "top" or "crest" of the hill, not the "base", IMO... Is there a diagram that goes with this problem?

 

[kuruman]

Unless by "base" they mean the top of the hill? That would usually be referred to as the "top" or "crest" of the hill, not the "base", IMO... Is there a diagram that goes with this problem?

One one hand, the question does not specify whether the positive direction is uphill or downhill so the number for the acceleration can have either sign. On the other hand, the question may have adopted the convention that "positive" means "in the direction of the velocity" which means the number must be negative. The question would have no ambiguity if it asked for the magnitude or if it specified which way is positive.