Force and constant veloicty?

Question

A man pushes on a piano of mass 180 kg so that it slides at a constant velocity of 12.0 cm/s down a ramp that is inclined at 11.0^\circ above the horizontal. No appreciable friction is acting on the piano. Calculate the magnitude and direction of this push

how can you have a constant velocity while applying constant force on a frictionless surface? am i missing something?

Answer 1

It is impossible.

If there is no friction, the piano will be subject to earth's gravity, which will increase the speed of the "fall" of the piano down the ramp as it moves farther down it.

Of course, some people work with "assuming" that this IS possible, so that may be what they are looking. Solving this based on the assumption that this is possible.

Try not to think about what really happens, try to think about what they are asking for.

Answer 2

The only logical interpretation of the question is that the man is pushing "uphill" against the pull of gravity making the problem physically sensible!
If the piano slides frictionless at constant velocity down the inclined plane it means that the man's force component parallel to the inclined plane is balancing (opposite and equal to) gravity's component in the oppisite direction along the inclined plane.

Answer 3

actually, you can assume that you have a friction less situation once that the object is supposed to be roller mounted and of course the ramp is smooth

the angle of the ramp is large enough to make the piano go down the ramp at a certain velocity

but is small enough to keep it under 12 cm/sec

what the problem wants is the force applied to make it roll constantly to 12cm/sec

Answer 4

Errmmmm....... Maybe they meant 'up' the ramp, in which case the force exerted would equal
9.8*180*sin(11) and would be parallel to the inclined plane.

Or he's supplying a force equal to that to hold the speed constant against the acceleration of gravity (without his force being exerted,the piano would accelerate)

That's all I can think of.


Doug