Force Homework Problems Checklist

I am given a problem where I am to pick up the prism shown below by touching only the upper two faces. The coefficient of friction with each face is 0.4 and the mass of the prism is 30grams. What is the minimum force I must apply to each face in order to lift the prism?

The one thing I am stuck on are the directions of the force I apply with my fingers. I am not sure whether

a)the forces exerted by my fingers act horizontally inwards (which is slightly confusing me; theoretically, should horizontal forces not be able to counteract the downwards weight of the prism? And yet my calculations in this case give a force required of 0.61N)

b)or whether they act exactly normal to the surface (in which case i get 0.22N)

c)or whether they can act directly up the slope straight away, or at least with some upwards inclination to counteract the weight.


Alright so I think I know how to do this but I require help in calculating what acceleration would be in terms of some sort of friction coefficient.

So model a particle going down a hill. The slope is 25 degrees. The mass of the particle is 50kg and the coefficient of sliding friction between the particle and slope is 0.05. When the brake is applied, 260N acts in the opposite direction to the motion of the particle. g = 9.8ms^-2

I won't write out my entire workings are they're lengthy, but I'll give the line I am up to which is:

let $\mu$ = the coefficient of sliding friction

let $b$ = the braking force

$ma_i = (mg \cos{65}-\mu bN)\hat{\mathbf{i}} + (N-mg \sin{65})\hat{\mathbf{j}}$

So I should imagine that b is going to slow down the acceleration, so perhaps it's as simple as 0.05 x 240?

I'm not sure if it would be 240 or 2.4 though, for example - any elucidation on this?


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