# Stone resting on a spring

1. Oct 13, 2004

### HobieDude16

I got parts a and b but am having trouble getting part c and d. can someone please help me? thanks in advance!

Figure 8-40 shows an 8.00 kg stone resting on a spring. The spring is compressed 8.0 cm by the stone.

Fig. 8-40

(a) What is the spring constant?
9.8 N/cm by mg/x(compression)

(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?
70.8 J by convert A to N/m then convert compression to m and then use .5kx^2 to get the answer

(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?
J gravitational potential energy is mgy but i don't know y

(d) What is that maximum height, measured from the release point?
m y=(.5mv^2)/mg I know i have to use this eqn. but i don't know v.

2. Oct 13, 2004

### vtech

parts c) and d)

(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?
*** as you said, J gravitational potential energy is mgy but i don't know y, but from conservation of energy you know that dU = EPinitial (see answer B)...

(d) What is that maximum height, measured from the release point?
m y=(.5mv^2)/mg I know i have to use this eqn. but i don't know v.

** actually you don't have to use this equation.... we know dU = mg dy = EPinitial.... and now you can solve for height..