Posted by Anonimus on Saturday, November 2, 2013 at 6:58am.
A meteorite of mass m= 2 ×104 kg is approaching headon a planet of mass M= 7 ×1029 kg and radius R= 5 ×104 km. Assume that the meteorite is initially at a very large distance from the planet where it has a speed v0= 5 ×102 km/s. Take G= 6.67 ×10−11.
Determine the speed of the meteorite v (in m/s) just before it hits the surface of the planet. (The planet has no atmosphere, so we can neglect all friction before impact)
v=

physics(URGENT!!!!!)  bobpursley, Saturday, November 2, 2013 at 9:10am
Intiial PE=GMm/r
Initial KE=1/2 m v^2
can you convert that intial energy to final ke? 
physics(URGENT!!!!!)  Anonymous, Saturday, November 2, 2013 at 9:20am
my final formula is: Vf=sqrt(Vi^2+(mMG/r))
r being the radius of the planet 
physics(URGENT!!!!!)  bobpursley, Saturday, November 2, 2013 at 9:23am
1/2 m vf^2=1/2 m vi^2+GMm/r
where r is the initial distance of the object. You can ignore the final PE, as the object is very far from the planet initiually. That does not lead to what you got. 
physics(URGENT!!!!!)  Anonymous, Saturday, November 2, 2013 at 9:29am
but isn't the object initially at r=infinity therefore P_i=0 and the potential energy just before impact Mmg/the radius of the planet? or am i completely of target

physics(URGENT!!!!!)  Sat, Sunday, November 3, 2013 at 3:07pm
1/2 m vf^2=1/2 m vi^2+GMm/r  it's correct!