# Physics

3)
a) Calculate the unstretched length of a spring, which has a Hooke's constant of 40N/m and is 56cm long when supporting a stationary 800g object.

I did
mag = kx
(0.800)(9.81) = 40x
x = 0.20m

l-x = u
56-20 = u
u = 36cm

Is that right?

b) The period with which the object would oscillate vertically.
I did
T = 2pi sqrt(0.800/40)
and got 0.9s...is that right?

c) The amplitude that would be required so that the object's maximum speed while oscillating would be 160cm/s. Then suggest why an oscillation is not possible with this spring.

I don't understand how to calculate that.

6) If a flea has a mass of 2.0x10^2 micrograms jumps vertically to a height of 65mm and 75% of the energy comes from elastic potential energy stored in the protein, determine the initial quantity of elastic potential energy.

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1. 3(a) and (b) look OK. For 3(c), use
(1/2)MVmax^2 = (1/2) kX^2 and solve for the maximum amplitude X. If X exceeds the unstretched spring length, such an oscillation is not possible, since you can't compress the spring to a negative length.

For (6), use
(1/2)M g H = (0.75)E where E is the potential energy stored in protein and H is the height that the flea can jump.

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2. I got 23cm using that formula for 3a. Should I add that to 36? I don't get it.

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