Homework Help: Static friction : Moving truck

1. Oct 22, 2007

Paulbird20

An un-tethered block sits on a flatbed truck as it accelerates up an incline that makes an angle of 15° with respect to the horizontal. If the truck speeds up at a rate less than 2.50 m/s2, the block remains on the truck. If the truck speeds up at a rate equal to or greater than this value, however, the block slides off the truck. What is the coefficient of static friction between the truck and the block?

Ok so i understand that tan(15) gives me the coef if the trunk is motionless i think? (.267)

And when it has motion i need to account for Normal Force which is Fn= M* G

But i cannot figure out how i get the mass. Assuming something to do with the 2.50 accel but i am stuck any tips would be great.

Fs = n tan angle also found that but still cant figure out how to get Fn

Last edited: Oct 22, 2007
2. Oct 22, 2007

Paulbird20

edit

Last edited: Oct 22, 2007
3. Oct 22, 2007

learningphysics

What is the maximum frictional force?

There are 3 forces acting on the block... the static frictional force upward... gravity, and the normal force...

sum of the forces in the direction parallel to the incline = ma

set a = 2.50. what is the frictional force?

sum of the forces perpendicualr to the incline = 0

what is the normal force?

so what is the coefficient of frction...

4. Oct 22, 2007

Paulbird20

ahhhhh i feel dumb =/ i got it now thank you for leading me in the right direction