Forces on an object falling to earth Question

[asura]

Homework Statement

As an object falls toward Earth

a. the object does not exert a force on earth
b. the object exerts a downward force on earth
c. Newton's third law does not apply
d. the upward acceleration of Earth is negligible because of its large mass

Homework Equations

none

The Attempt at a Solution

I chose A, but the answer for this question is d. Can someone explain how Earth accelerates?

 

[paradigm]

Two bodies in space always exert a gravitational force on each other, F = (G*m1*m2)/r^2 which pulls each body towards the other... this is Newton's third law, the postulate of equal/opposite forces... if the Earth exerts on a gravitational force on a falling object, that same object must reciprocate and pull on the Earth as well. this force is just far too weak for the Earth to accelerate appreciably

 

[Dick]

Newton's third law. The object exerts a force on the Earth equal and opposite to the force the Earth exerts on the object. Now reconsider d). Why doesn't the Earth jump up to meet the object?

 

[asura]

ok, I understand now. I forgot gravity also had an opposite force.

thanks