physics
posted by Riya on .
Luke is trying to catch a pesky animal that keeps eating vegetables from his garden. He is building a trap and needs to use a spring to close the door to his trap. He has a spring in his garage and he wants to determine the spring constant of the spring. To do this, he hangs the spring from the ceiling and measures that it is 19.1 cm long. Then he hangs a 1.10kg brick on the end of the spring and it stretches to 40.1 cm.
This question exist of 4 parts I finished a and b, but still need c and d! Anyhow I am not getting the right answer someone please help.
(c) When the displacement is 2.55 cm from the equilibrium position, what is the speed of the brick?
(d) How long will it take for the brick to oscillate five times?
Thanks!

The spring constant is
k = M*g/0.21 m = 51.3 N/m
(c) The sum of kinetic and (spring) potential energy is constant. The answer depends upon how much the spring was stretched before it was released and set in motion. You did not provide that information.
The oscillation period is
P = 2*pi*sqrt(M/k) = 0.92 seconds
It will take five tinmes that to osciallate five times, no matter how much it was initially stretched. 
a)(a) What is the spring constant of the spring?
51.3 N/m
(b) Luke now pulls the brick 5.1 cm from the equilibrium position to watch it oscillate. What is the maximum speed of the brick?
.35 m/s
So would you subtract 2.55 cm from 5.1 cm? To get how much was stretched?