Physics: Help with Work(concept) When is it applied? 10PTS!!!
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Physics: Help with Work(concept) When is it applied? 10PTS!!!

[From: ] [author: ] [Date: 12-06-17] [Hit: ]
so no work.B) constant velocity means no acceleration. That means no net force, since net force = m * a. The word frictionless is important here. Since theres no frictional force,......

But you can do work without accelerating something. I'll explain in a second.

A man pushes against a wall: No displacement, so no work.
A) No displacement, so no work.
B) "constant velocity" means no acceleration. That means no net force, since net force = m * a. The word "frictionless" is important here. Since there's no frictional force, then "no net force" means there's no force at all acting. So F = 0, and there's no work.

BUT if there were friction, you would be exerting a force. "No net force" means the force you're providing is countered by friction. And the work F * d you're doing is going into heat from friction rather than into accelerating the object. You're still doing work. You're putting energy in.

C) There's a force (gravity) and displacement in the direction of the force. So there's work. Yes, it accelerates. It got energy. That energy came from the gravitational force doing work.

Next group:
A) If "overcome gravity" means "move upward", then yes. There's a force, and there's a displacement. If it just means "hold it up" like A above, then no.
B) Yes. The object is getting energy by something doing work on it.
C) Yes. See my discussion above. Something is putting energy into the system, and friction is doing work to take it out again. No net gain in energy.

Perhaps it would help to think in terms of energy rather than acceleration.

-
Energy Used = Work = Force * distance.

Acceleration has nothing to do with it.

Consider: A box moving at constant velocity against friction the force is doing Work, though the box is NOT accelerating.

W = 10 N of friction * 10 meters the box is pushed at constant velocity = 100 Joules of Work

Student pushing against the wall, the wall does not move ===> No Work.

A: No Work, the object does not move
B: No Work, by Newton's 1st Law no force is acting on the object on a FRICTIONLESS surface. If there was friction then as explained above there would be Work
C: The object falls freely, the Potential Energy is converted to Kinetic Energy, no energy used ===> No Work

Sorry, my dog said he had to go.

All 3 are Work

A: Lift an object increasing its Potential Energy
B: To accelerate the object you must apply a force, so you do Work for the distance the Force is applied
C) As stated before. Pushing a distance against friction is Work
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