Frames of Reference: Using tie-downs to hold a load on a flatbed truck

[daisy7777]

Homework Statement

A flatbed truck has a 2000.0 kg component of a pre-fab house placed on its flatbed. If the coefficient of static and kinetic friction, respectively, between the pallet and the flatbed is 0.150 and 0.100, and the truck starts at rest and accelerates to a speed of 65.0 km/h over a distance of 50.0 m. The component is strapped down by tie straps wrapped over the top of the house component so as to push down on it; with what force must the tie straps push down on the house component in order to prevent the truck from slipping while accelerating?

Relevant Equations

Fnet = ma, Ff = coeff of friction * normal force, Fnet = 0 when not accelerating

I calculated the net force. I got 6500. I determined this is bigger than the force of static friction so the force of friction acting on the object must be kinetic. From there I got kinda lost. I know for the component to not slip Fnetx = 0 and Fnety = 0. But I'm not sure what to do from there? Is it (in the y-dir) 0 =Fn - Fstraps - Fg? Or (in the x-dir) 0=Ff+Ffict-Fstraps?

 

[haruspex]

this is bigger than the force of static friction

What is the normal force? Don't forget the straps.

 

[daisy7777]

What is the normal force? Don't forget the straps

Wait so the force of friction is gonna be Ff = coeff of friction * (Fstraps + Fgravity)?

 

[haruspex]

Wait so the force of friction is gonna be Ff = coeff of friction * (Fstraps + Fgravity)?

Yes. If the magnitude of the normal force were only Fg then you would have Fg acting up on the slab but Fg+straps acting down on it, so it would be accelerating downwards!