# physics(URGENT!!!!!)

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A meteorite of mass m= 2 ×104 kg is approaching head-on 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!!!!!) -

Intiial PE=GMm/r
Initial KE=1/2 m v^2
can you convert that intial energy to final ke?

• physics(URGENT!!!!!) -

my final formula is: Vf=sqrt(Vi^2+(mMG/r))
r being the radius of the planet

• physics(URGENT!!!!!) -

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!!!!!) -

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!!!!!) -

1/2 m vf^2=1/2 m vi^2+GMm/r - it's correct!

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