How much work does the earth do? help

[ohheytai]

A mass of 0.105 kg hangs from a vertical spring in the lab room. You pull down on the mass and throw it vertically downward. The speed of the mass just after leaving your hand is 5.20 m/s.

(a) While the mass moves downward a distance of 0.06 m, how much work was done on the mass by the Earth? Include the appropriate sign

(b) At the instant in part (a) when the mass has moved downward a distance of 0.06 m, the speed of the mass has decreased to 3.74 m/s. How much work was done on the mass by the spring? Include the appropriate sign.

can someone help me? I've tried this twice and i missed it twiceee someone show me how please!

 

[lvslugger36]

a) Work = Fd when they're in the same direction. So the force on the mass is mg (.105 x 9.8), and the distance it moves down is .06 meters. So solve for Fd (they're in the same direction so the answer is positive).

b) We'll write that the spring and Earth do work on the mass: so -1/2kx^2 + mgh = Net work

-.5 kx^2 + mgh (the solution to a) = 1/2m(vf)^2 - 1/2m(vo)^2. All you have to do is solve for -.5 kx^2. The work is negative because the displacement is downwards and the force is upwards.

 

[ohheytai]

ok thankss!