Question

In order for work to take place

the energy present must be related to the movement of the object.

the force applied must be a balanced force resulting in motion of the object.

the force applied must cause the movement of the object in the same direction as the force.

the movement of the object must be the cause of the force.

Answer 1

I think C.

Answer 2

\[Work=Force \times distance\]That should give you the answer.

Answer 3

Hmm i don't think that helps much :P.. cause of options C and D.. which one do you think it is?

Answer 4

D cannot be correct since it states that "the movement of the object MUST be the cause of the force".

Answer 5

In addition, (positive) work can only be done when the force causes the object to move in the same direction as the force. Everything points to C.

Answer 6

wrong.. answer is D

the displacement need not be in the direciton of the force.. simple example?.. a block sliding on a slope.. gravity is acting downward, but still the object displaces along the slope :P

answer is D.. cause the movement HAS TO BE cause of that force.. else no work is said to be done!

Answer 7

Movement is the *result* of a force...not the *cause* of it. The answer is definitely C.

I refer you back to the definition of work which can be found in any first-year physics book:
http://en.wikipedia.org/wiki/Work_%28physics%29
http://hyperphysics.phy-astr.gsu.edu/%E2%80%8Chbase/work2.html

Regarding your block/incline example:
The horizontal movement of the block has absolutely no bearing on the amount of work done by the force of gravity (W=F*d=mgh) because the horizontal motion is perpendicular to the (strictly) vertical force of gravity.

A related example would be a person carrying a block across a room without changing it's height. They could carry that block for miles and the amount of work they've done would still be exactly 0J (ignoring friction). This is because the force they are applying to the block is vertical to keep it at some height and the direction of motion is horizontal.

In short, effort does always not equate to how much work is done in a physics-sense. Work is a purely mathematical calculation. An applied force must have some component that is in the direction of motion for work to have been done.

Answer 8

exactly.. it should have SOME COMPONENT of motion in that direction...

but look at option C ... it says THE ENTIRE motion must be in the same direction as that of the force..so thats not a necessity..

and what do you mean movement is the RESULT of force and NOT the cause of it.. ? :P.. I still go with D..

@yrelhan4 @rajathsbhat

lets see what they have to say!

Answer 9

nope. i dont think the answer is C. another example. lets say a block compresses a spring. the direction of force is opposite to the direction of the motion of ball until it stops.
another. a ball rolls on the floor, stops after some time. friction is acting opposite to motion of the ball. so friction does work on the ball to stop it. so answer cannot be C.

Answer 10

C says: "must cause the movement of the object in the same direction as the force. " I don't see the word "entire" movement in that anywhere.

Answer 11

Regarding the other part... Movement is the result of a force. In your earlier post you stated that the object is causing the force...at least that's how I read it earlier.

Maybe I misunderstood what you meant there :)

Answer 12

'must' cause in the same direction isnt correct.

Answer 13

For positive work...which I assume is what is meant in the question, C's wording would be correct.

Answer 14

yes positive work. but i suppose they are talking about work in general.

Answer 15

They could have worded it better, I agree

Answer 16

Probably a High School physics class :)

Answer 17

Hey they never said POSITIVE work

and besides for positive work, the angle between them must be acute thats all :P..

Answer 18

I give up :)

Answer 19

Could have worded the question better.