# Easy Acceleration / Friction question

• dglenn9000
In summary, Homework Equations state that the total force (in the direction of the slope) is equal to the mass times the acceleration. If the friction between the box and the roof is .15, then the box will move at an acceleration of .70 m/s2.f

## Homework Statement

A roof has an incline of 10 degrees. If the µ of friction between a 50kg box and roof is .15, how fast will the box move?

Ff=µ * Fn

## The Attempt at a Solution

I have no idea how to get this. I know it very easy.
I figured out Fg = 490N (Fg=9.8 * 50kg)
I figured out Fn = 482.56 (Fn=490 cos 10)
I figured out F//=85.09 (F//=490 sin 10)

I figured out the Acceleration with no friction is 1.70 m/s2 85.09/50

Any help is appreciated, thanks

Last edited:
Welcome to PF!

Hi dglenn9000! Welcome to PF! A roof has an incline of 10 degrees. If the µ of friction between a 50kg box and roof is .15, how fast will the box move?

Hint: just use good ol' Newton's second law …

total force (in the direction of the slope) = mass times acceleration I have a questions : there is an air track and on that track there is a body at rest upon which acts a constant force for a given time it gains a velocity. My question is if that force acts again upon that body for that amount of time will the velocity be 2 times the first velocity? My opinion is that starting from Newtons law v=v0+at, but if we use two times this quation we obtain that v1=at+at=2v0. Am I right?

Welcome to PF!

Hi DIrtyPio! Welcome to PF! … a constant force for a given time … if that force acts again upon that body for that amount of time will the velocity be 2 times the first velocity? My opinion is that starting from Newtons law v=v0+at, but if we use two times this quation we obtain that v1=at+at=2v0. Am I right?

yes, but it's better to look at it from the words of Newton's second law …

force = rate of change of momentum = mass times rate of change of velocity,

so (from the meaning of "rate of change") ∫force times time = mass times change of velocity. Hi dglenn9000! Welcome to PF! Hint: just use good ol' Newton's second law …

total force (in the direction of the slope) = mass times acceleration That is how I got how fast it will move without friction.

a= F/m
1.70 m/s2= 85.09/50kg

But my question is how do I figure out the acceleration with friction of .15? Where do I apply the .15 in my equation?

Hi dglenn9000! just woke up :zzz: …
… Where do I apply the .15 in my equation?

You multiply it by the normal force to get the (magnitude of the) friction force: Ffriction = µN.

You then chuck the friction force into the "total force" in Ftotal = ma Hi everyone do you do any problems considering phyisc?