# M1 help- Friction

• Mar 28th 2010, 01:46 PM
fishkeeper
M1 help- Friction
I cant seem to know where to start on this question:

Quote:

A block is thrown down a slope inclined at 35 degrees to the horiztonal. It's initial velocity is $8ms^1$ and the coefficient of friction between the block and the slope is 0.8.
How long does it tale for the block to come to rest?
How do I try to start this please? I am thinking we may need to find the resistive force F and then use this to try and find a mass? And then use SUVAT to work out the time?

I am completely clueless it has to be said, and it would be amazing is anyone could possibly gie me some helpful pointers on where to go with this question?

many thanks, I will + rep you :D
• Mar 28th 2010, 02:02 PM
skeeter
Quote:

Originally Posted by fishkeeper
I cant seem to know where to start on this question:

A block is thrown down a slope inclined at 35 degrees to the horiztonal. It's initial velocity is http://www.mathhelpforum.com/math-he...6dc08c8d-1.gif and the coefficient of friction between the block and the slope is 0.8.
How long does it tale for the block to come to rest?

$F_{net} = ma$

$mg\sin(35) - (0.8)mg\cos(35) = ma$

$g\sin(35) - (0.8)g\cos(35) = a$

you also have $v_0 = 8$ m/s and $v_f = 0$ ... find $t$
• Mar 29th 2010, 04:13 AM
fishkeeper
Thankyou Skeeter

I have followed your working and am glad to say I have understood

I completed this working:

http://www.mathhelpforum.com/math-he...8caa8730-1.gif

I then got for a value of acceleration -0.80ms^2

As there was then $u=8, v=0, a= -0.8, t=?$

I then used v=u+at, rearranged to get $t= \frac {v-u} {a}$

$\frac {0-8} {-0.8} = 10s$

Is that the correct answer (Im just making sure)

Thanks so much!!!