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Work Done by Spring

  • #1

Homework Statement



An ideal spring is hung vertically from the ceiling. When a 3.0 kg mass hangs at rest from it the spring is extended 9.0 cm from its relaxed length. An upward external force is then applied to the block to move it upward a distance of 12 cm. While the block is being moved by the force, the work done by the spring is:

-1.2J, -0.52J, -0.26J, 0.52J, 1.2J

Homework Equations



Hooke's law: F(spring) = -kd
W(spring) = 1/2kx(initial)^2 - 1/2kx(final)^2
Wapplied = -Wspring (assuming stationary before and after displacement)

The Attempt at a Solution



I think I can plug in 9 as x(initial) and -3 as x(final), giving me:
W(spring) = 1/2k81 - 1/2k9 = 40.5k-4.5k = 36K
so W(spring) = 36K

Not sure what else to do yet
 
Last edited:

Answers and Replies

  • #2
Kurdt
Staff Emeritus
Science Advisor
Gold Member
4,812
6
You need to work out the spring constant and converting from cm to meters might help. Also the spring is not at its natural equilibrium point when the mass is hung. It already has some potential energy.
 

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