A block on the platform of an acceleratin truck

[lep11]

Homework Statement

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.

Homework Equations

displacement x=½at^2
F=ma
F_μ=Nμ=mgμ

The Attempt at a Solution

ƩF_x=ma
F_μ=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.

 

[Doc Al]

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.

Right. (Assuming the truck starts from rest.)

I suppose the only force accelerating the block is static friction, am I right? And truck and block are accelerating at the same rate.

Right.

I used to be good at these but...well...maybe I need little revision before the final exam.

A bit of review never hurts.

 

[lep11]

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