Question

a student pushes a 40-n block across the floor for a distance of 10 m. how much work was applied to move the block

Answer 1

W = Fd
= (40)(10)
= 400J

Answer 2

@amonoconnor
I think this is not correct

40N is the weight of the block.

The pushing is sliding it across the floor - so the force to move it in NOT 40N

You need to knw the coefficient of friction to solve this - because the work done is against friction , not against the weight of the block

Answer 3

I agree with that, but because the information posted was so basic and didn't involve those concepts, I thought it was perhaps an easier problem, and since to push the block you would have to push it is weight, that might make sense, when only first learning about these concepts.

Answer 4

I don't think that is a valid assumption.

The question should state the force required to move the block, NOT its weight.

As it is phrased, this question cannot be answered correctly

Answer 5

Okay. :)

Answer 6

BTW the friction force shown as mu * N

N is the Normal reaction force = 40N

Answer 7

@crissy77
Work done = Force * (distance moved IN DIRECTION OF FORCE)

In your question - the weight is vertically down, and the motion is horizontal. So no work is done against the weight. Any resisting force (the friction) can be calculated if you know mu ( the coefficient of friction)
If the floor is 'frictionless' or 'smooth' as sometimes used in simple questions then the resisting force is 0 and hence work done is 0

Answer 8

I am pretty sure, with the information given, that this task is considered frictionless. It would also not make much sense for the exercise to provide the weight in Newton; it was probably meant as the force required to push it 10 meters.

Thus bringing us back to the origin; \[W = Fs\](Work = Force * displacement)

W = 40N x 10m = 400J

Although I must admit; the elaboration of the question makes it difficult to give an exact answer. :P

Answer 9

NO - this is still incorrect

IF the surface is frictionless then NO work (0 Joule) is done by moving the block across a horizontal floor

I refer you to my earlier reply.

NO work is done against the weight of the block (assuming the floor is horizontal) so the weight of the block is not the force exerted.

IF you were LIFTING the block by 10 m THEN you would do 400J work but MOVING it horizontally does NOT do this amount of work. It is either zero (if smooth) OR 10 * mu *40 if coefficient of friction is mu.

This is unfortunately a badly phrased and unanswerable question.

Answer 10

@Ivanskodje

Answer 11

Oh right... ! If it were no friction, then the weight and force required to push it would e irrelevant @_@ I see the light!

Answer 12

Yes - the free body diagram I drew above shows the forces on the block.

The weight acts vertically down, and is resisted by the EQUAL force N (normal reaction force)

The pushing force is resisted by the friction, and the work done by the pushing force is ONLY against friction.

Without knowledge of mu this cannot be answered.