If you could place an 80Kg rock at the same distance from the Sunas the earth, b

Question

If you could place an 80Kg rock at the same distance from the Sunas the earth, but freeze its orbital motion so that it felldirectly toward the Sun when released, how fast would it be goingafter the first 2 million miles? Assume you are far away from otherplanets

You would use the law of gravitation formulaGMsunMrock/R2 to find the force ofgravity b/t sun and rock.

G = 6.67 x 10-11 N m2/kg2
Mass of Sun = 1.99 x 1030 kg

I'm not sure what would R be? Wouldn't that be the distancebetween the rock and the sun which would basically be the distancefrom earth and the sun? In the problem it says as a side notethat R is not a constant and that I may assume the appropriate avgacceleration.

The distance the earth is from the sun is 1.50 x 1011 m..but I'm not sure if I'm supposed to use it in this problem sinceR supposedly isn't a constant?

Explanation / Answer

here we assume that the distance is constant . then gravitational force F =GMsunMrock/R2 Accleration of the rock a = [GMsunMrock/R2 ] / Mrock                                       = GMsun/R2 where R = 1.5 * 10 ^ 11 m Initial speed u = 0 distance S = 2 millon miles = 2 * 10 ^ 6 miles                 = 2 * 10 ^ 6 * 1609 m from the relation v ^ 2- u ^ 2 = 2aS                                      v = [ 2aS ] plug the values weget answer i.e., v value                          

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