The object does not move.
Answer:
Average speed, 
Explanation:
Given:
- Initial speed, u=40 cm/s
- final speed , v=20 cm/s
- Time taken, t=5 s
<u>First case</u>
Using equation of motion we have

Now using,

now putting the value of a in first equation we get

<u>Second case</u>
Acceleration
Time taken 
using equation of motion in one Dimension we have

Average speed is equal to total distance travelled per unit total time taken

Gravitational Force is F=G*m1*m2/r^2
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