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How can you calculate the work done by a force (of unknown quantity) exerted on a 10kg block on an inclined plane. The force is pointing upwards and parallel to the incline (which is inclined 30 degrees with respect to the horizontal).

a. frctionless plane b. coefficient of friction = 0.12

So the forces acting the block are the normal force, its weight, the friction force (for letter (b)), and the force exerted upwards the incline. All are given or can be solved almost instantly except for the force upwards denoted by F.

How do I solve this problem? I am not sure what value of acceleration to use in the axis of the incline for F=ma. Sorry I could not provide a diagram for this.

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closed as off-topic by ja72, Brandon Enright, Chris White, WetSavannaAnimal aka Rod Vance, Kyle Kanos Feb 4 at 2:53



Sounds like homework. Figure out the force if it is frictionless, then add in the friction force, multiply by distance. Forget F=ma - you figure out why. –  Mike Dunlavey Feb 3 at 18:51
(a) is the case where the plane is frictionless while in (b) there is friction. I still don't get it. How can I solve for the value of F? I think I'll be using it to solve for work W=(Fx)(d) where d=5m by the way. What value of a in the direction of the plane will I use? @MikeDunlavey –  mc8 Feb 3 at 18:58
Draw a vector diagram of the forces, and use a smidge of trig. –  Mike Dunlavey Feb 3 at 19:58
Must I make use of the PE and KE in solving for the work done by F? I've done that. But without the x component of the accleration and the value of F, I don't think I can solve for W. But the y component of acceleration is zero right? @MikeDunlavey –  mc8 Feb 3 at 20:10

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OK, I'll help you this far. Here's the diagram you should be able to make, and figure out everything else from that. I purposely put in ?? so you can't just hand it in and pretend you did it.

enter image description here

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I seriously don't understand why I don't need to use the F=ma. I mean it's the most fundamental equation in solving applications of Newton's laws. Plus I don't know the value of F and a???? –  mc8 Feb 3 at 21:39
@mc8: because you're not accelerating. It's a simple balance of forces. –  Mike Dunlavey Feb 3 at 21:40
so Fnet=0???? Isn't it that W=Fd? How did you know that forces are balanced? –  mc8 Feb 3 at 21:44
How did you know there is no acceleration? –  mc8 Feb 3 at 21:45
@mc8: Because the work done is the same whether it is done in one minute or in one millenium. In the frictionless case, the weight rises through a distance, increasing its potential energy, and that is the work done. Please figure out the rest of it yourself. –  Mike Dunlavey Feb 3 at 21:50
