# Homework Help: The Forbidden 'F' Word

1. Oct 26, 2004

### 7C0A0A5

In the image {08_53.gif}, a block is moved down an incline a distance of 5.0 m from point A to point B by a force F that is parallel to the incline and has a magnitude of 2.3 N. The magnitude of the frictional force acting on the block is 10 N. If the kinetic energy of the block increases by 35 J between A and B, how much work is done on the block by its weight as the block moves from A to B? In Joules

--I'm not sure how to go about this problem...it looks like the masses drop out somewhere. But I don't understand how to get the answer. Also..is this looking for the work done by friction?

The image {08_35.gif} shows an 8.00 kg stone resting on a spring. The spring is compressed 7.0 cm by the stone.

(a) What is the spring constant?
The answer to this question is 11.211428571428571428571428571429 N/cm
(Sorry, got carried away with the digits )

(b) The stone is pushed down an additional 30.0 cm and released. What is the elastic potential energy of the compressed spring just before that release? In Joules

(c) What is the change in the gravitational potential energy of the stone-Earth system when the stone moves from the release point to its maximum height? In Joules

(d) What is that maximum height, measured from the release point? In meters

--So if I find (b), then (c) would be mgh, where h = the height to equilibrium right?
--and then (c) would be....duh...'h' plus 30 cm
--So if I'm understanding both (c) and (d) correctly the only thing stopping me is (b). So if you could give me a "huge" shove inthe right direction . I'd be obliged.

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