Really stuck on a Gravitation Question

[grantP]

Homework Statement

What minimum energy is required to raise a 1.7e3 kg vehicle from the surface of the moon to a height of 5.22e6 m?

Homework Equations

Ep= -G(m1m2)/r

The Attempt at a Solution

Ep(initial)= -6.67e^-11(1.7e^3 x 7.35e^22)/1.74e^6 = -4789750000

Ep(final)= -6.67^-11(1.7e3 x 7.35e^22)/6.96e^6= -1197437500

I have tried subtracting the final by the initial, but I am not getting the correct answer of 3.6e^9 J.

 

[alphysicist]

Hi grantP,

Homework Statement

What minimum energy is required to raise a 1.7e3 kg vehicle from the surface of the moon to a height of 5.22e6 m?

Homework Equations

Ep= -G(m1m2)/r

The Attempt at a Solution

Ep(initial)= -6.67e^-11(1.7e^3 x 7.35e^22)/1.74e^6 = -4789750000

Ep(final)= -6.67^-11(1.7e3 x 7.35e^22)/6.96e^6= -1197437500

I have tried subtracting the final by the initial, but I am not getting the correct answer of 3.6e^9 J.

What are you getting? It looks to me like if you do Ep(final) - Ep(initial) you do get 3.6 x 10⁹J.

 

[grantP]

oh...hmmmm i must have mixed up my signs...and doing 4 straight hours of physics homework probably didnt help...looking back at it 4 hours later I was probabaly so delerious haha.

Well anyways thanks for the help on my threads.

 

[alphysicist]

Right, I understand completely about how too much work can make you start seeing things. Glad to help!