# Homework Help: A block on the platform of an acceleratin truck

1. Jan 31, 2013

### lep11

1. The problem statement, all variables and given/known data
A block is on the platform of an accelerating truck. The coefficient of static friction between the block and the platform is 0,25. What is the minimum time in which the truck can accelerate so that the block won't slide. During the acceleration the truck travels 75 meters.

This was a bit difficult at first sight but I know I have to find the max acceleration of the block and then calculate the minimum time using equation x=½at^2.

2. Relevant equations
displacement x=½at^2
F=ma
Fμ=Nμ=mgμ

3. The attempt at a solution
ƩFx=ma
Fμ=ma
mgμ=ma
a=gμ=.....Eventually I got ~7,8s.
I suppose the only force accelerating the block is static friction, am I right? And truck and block are accelerating at the same rate. I used to be good at these but...well...maybe I need little revision before the final exam.

Last edited: Jan 31, 2013
2. Jan 31, 2013

### Staff: Mentor

Right. (Assuming the truck starts from rest.)
Right.
A bit of review never hurts.

3. Jan 31, 2013

### lep11

Thank you for a quick reply. I forgot to mention it starts from rest.