Two Physics problems related to gravitational energy

AI Thread Summary
To determine the speed a rocket must achieve to reach a maximum height of 895 km above Earth's surface, the required velocity is 3920 m/s. For achieving an orbit at the same altitude, the rocket must reach a speed of 8380 m/s. The discussion highlights the use of gravitational energy equations, specifically EG = -GMm / r, to calculate these velocities. Participants emphasize the importance of understanding the differences in energy states between vertical ascent and orbital motion. The conversation underscores the need for clarity in calculating initial and final potential energy to solve these physics problems accurately.
chroncile
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Homework Statement


1.) How fast must a rocket leave the Earth’s surface to reach a maximum height of 895 km above the surface of the Earth (assume the rocket is simply going straight up)?

The answer is 3920 m/s

2.) How fast must a rocket leave the Earth’s surface to reach an orbit with an altitude of 895 km above the surface of the Earth?

The answer is 8380 m/s


Homework Equations


EG = -GMm / r


The Attempt at a Solution


For 1.)

Ek + EG = Ek' + EG'
0.5v2 = GM / r
V = square root ((2 * G * 5.97*x10^24)/895000+6370000)
V = 10,470 m/s

For 2.)

I have no idea
 
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What you did for `1,' was you found the energy the rocket needed to end up with, then you figured out what velocity that corresponds to. You can do the same thing for `2,' just think: what's different about the final energy of the rocket in '2' as apposed to '1.'
 
But I didn't even get the right answer in question 1.
 
chroncile said:
But I didn't even get the right answer in question 1.
Good point. What is the initial potential energy? Then what is the final?
 

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