Sorry to bother with yet another question today, but I'm a little lost with this one.(adsbygoogle = window.adsbygoogle || []).push({});

QUESTION

A box with a mass of 25 kg is at rest on a ramp inclined at 45 degrees to the horizontal. The coefficients of friction between the box and the ramp are us=0.78 and uk=0.65.

a) Determine the magnitude of the largest force that can be applied upward, parallel to the ramp, if the box is to remain at rest.

b) Determine the magnitude of the smallest force that can be applied onto the top of the box, perpendicular to the ramp, if the box is to remain at rest.

MY ANSWER

a) Fa = Fgh + Ff

= Fg sin 45 degrees + usFn

= (22kg)(9.8 m/s^2)(sin 45 degrees) + (0.78)(22kg)(9.8 m/s^2)(cos 45 degrees)

= 271 N

Therefore the largest force that can be applied upward if the box is to remain at rest is 271N.

(I believe this may be incorrect as gravity/normal are balanced and only the force of friction is impeding which would be 118.9N, but I wanted to double check)

b) I'm really not sure where to start with this as there has not been an example like with with my text :( Could someone give me a hint?

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# Homework Help: Static Friction, stuck on a problem

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