Posted by **David** on Tuesday, April 19, 2011 at 10:19am.

Law of Gravitation- Find an expression for the magnitude of the initial velocity that a projectile must possess in order to leave the earth when air friction is neglected. The gravitational constant for g is, G = 6.67428*10^-11 m^3 Kg^-1 s^-2

(10 marks).

Kind Regards

- Maths and Physics -
**bobpursley**, Tuesday, April 19, 2011 at 10:25am
I wonder what leave the Earth means. If it means to escape the normally inevitable return to Earth, the normal way to find this is to Integrate the potenial energy from Earth to infintity. I am not certain you have had calculus.

NeededEnergy= INT GMe/r dr from r=re to infintity

then, having that number set

1/2 massprojectile*velocity^2 equal to it, and solve for velocity. this is often called "escape velocity"

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