Statics problem with friction

Question

raffle_snaffle · Answer

attachment

raffle_snaffle · Answer

Problem states: Two 10* wedges of negligible weight are used to move and position the 400-lb block. Knowing that the coefficient of static friction is 0.25 at all surfaces of contact, determine the smallest force P that should be applied as shown to one of the wedges.

raffle_snaffle · Answer

@ganeshie8

raffle_snaffle · Answer

@dan815

surry99 · Answer

You have forgotten the normal force and frictional force from the wall which act on the 
400 lb weight.

surry99 · Answer

When you include these and solve , you get P = 313 lb.

raffle_snaffle · Answer

how does the wall affect the block or top wedge? I see the normal force though

raffle_snaffle · Answer

I mean how is there frictional force?

raffle_snaffle · Answer

oh... wait I see now.

surry99 · Answer

yes...the block wants to slide up the wall...hence there must be a frictional force and normal.

raffle_snaffle · Answer

Did you get Fn2=416.86lb and Fn3=-30.24lb 

Fn3 is the normal force from the wall and Fn2 is the force acting on the top wedge

raffle_snaffle · Answer

This isn't working... I swear my equations are right...

surry99 · Answer

I got N2 = 478 lbs, F2 = 120
N1 = 450 lbs, P = 313 lb.
Do you want me to scan the solution and post it?

raffle_snaffle · Answer

yeah i missed a sign...

surry99 · Answer

ok I will scan and post ...hang on...

raffle_snaffle · Answer

no don't scan the solution I got this. I mislabled a sign. This problem has really bothered me cuz i've been working on it for a few hours and started to get frustrated.....

raffle_snaffle · Answer

I got the same N2... Let me work it out.

surry99 · Answer

ok

raffle_snaffle · Answer

Yes got it!