## Physics QBank Question #17

muntahaali
Posts: 2
Joined: Sun Jan 06, 2019 1:27 pm

### Physics QBank Question #17

A 10-kg sled rests on a 30° ramp with a coefficient of static friction of 0.5. An upward force is applied to the sled, parallel to the slope of the ramp, in incremental values until the sled begins to accelerate up the ramp. Approximately what minimum force is required to perform this action?

Can someone please explain this question to me?
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NS_Tutor_Mathias
Posts: 616
Joined: Sat Mar 30, 2019 8:39 pm

### Re: Physics QBank Question #17

In order to accelerate the sled up the ramp you will need to overcome the force of static friction and the component of the force of gravity acting parallel to the ramp.

So we just go ahead and find what those are:

Code: Select all

``````Framp = mgsin(30) = 100*0.5 = 50 N
Fstatic = mgcos(30)*mu = 100*0.87*0.5 = 43.5 N
Fopposing = 93.5 N
``````
So the minimum force to make the box start moving is at least 93.5 N, or about 95 N.

In essence, you have to push the box hard enough to overcome gravity to get it going - but you also, on top of that, have to overcome the force of static friction keeping it in place.