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# Any smart Physicists awake? Work done on a frictionless inclined plane help! watch

1. An object of mass 12kg is pushed 34m up a frictionless slope that is at an angle of 56 degrees to the horizontal

(a) work done on object?
(b) change in gravitational potential energy

It would be awesome if you could give me the answers!

my thoughts:

(a) w=fd so will it be 12 x 9.81 x 34cos56?
(b) gpe=mgh=12 x 9.81 x 34sin56?
2. (Original post by zezno)
An object of mass 12kg is pushed 34m up a frictionless slope that is at an angle of 56 degrees to the horizontal

(a) work done on object?
(b) change in gravitational potential energy

It would be awesome if you could give me the answers!

my thoughts:

(a) w=fd so will it be 12 x 9.81 x 34cos56?
(b) gpe=mgh=12 x 9.81 x 34sin56?
Looks right to me, but then again it's 1:30 so my eyes may be deceiving me
3. Right .
4. Wrong

They're both sine. They have to be the same.
5. (Original post by RogerOxon)
Wrong

They're both sine. They have to be the same.
Really? ohhhhh
6. (Original post by RogerOxon)
Wrong

They're both sine. They have to be the same.
I get the GPE = mgh one. But the work done I don't. I know the force has to be in the same direction as the distance. Distance is along the slope, is the force acting vertically or horizontally?
7. The component of the block's weight parallel to the plane is mgsin(56) - that's what you're pushing against. The component perpendicular is mgcos(56), but that would only be needed if we wanted to calculate the friction, but there isn't any.

The work to push it up the inclined plane is therefore mgdsin(56).

The gain in gravitational potential energy is mgh, where h = dsin(56).

If the two were not equal, where would the energy go / come from? There's no fiction or other mechanism for energy to be lost / gained.
8. (Original post by RogerOxon)
The component of the block's weight parallel to the plane is mgsin(56). The component perpendicular is mgcos(56), but that would only be needed if we wanted to calculate the friction, but there isn't any.

The work to push it up the inclined plane is therefore mgdsin(56).

The gain in gravitational potential energy is mgh, where h = dsin(56).

If the two were not equal, where would the energy go / come from? There's no fiction or other mechanism for energy to be lost / gained.
Thanks I get it!

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