# I Energy needed to launch a spaceship into Space

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1. Jan 20, 2016

### IsakVern

A given planet has a mass, M = 6.42*10^23 kg,
and radius, R = 3.39 * 10^6 m.

The gravitational konstant is G = 6.67*10^-11

A spaceship with mass m = 4000 kg is launched from the planets surface.

How much energy is needed to send the spaceship to a height h = 100 km above the planets surface?

2. Jan 20, 2016

### Buzz Bloom

Hi Isak:

There are several ways to approach this problem. One way is to calculate the potential energy of the spaceship at the height of 100 km. That is the amount of energy that has to be added to get the spaceship to that height.

First, the problem statement is a bit unclear. What is the assumed state of the spaceship when it reaches a height of 100 km. Here are two possibilities:
a) the spaceship is in orbit around the planet.
b) the space ship has zero velocity and will begin its fall back to earth.​

Hope this helps.

Regards,
Buzz

3. Jan 20, 2016

### IsakVern

The assumed state of the spaceship is that it has zero velocity when it reaches 100 km.

4. Jan 20, 2016

### Buzz Bloom

Hi Isak:

In that case I suggest you calculate the potential energy. You might find the following of some use. See the formula in the second box.
You may find the minus sign puzzling. If so, see what your textbook says about potential energy.

Regards,
Buzz

5. Jan 20, 2016