How to Solve for J and m in the Impulse-Momentum Theorem?

[lanky011]

(a)Use the impulse-momentum theorem to find how long a falling object takes to increase its speed from 4.5 m/s to 14.5 m/s

(b) J=mΔv

(c) I have 2 unknowns...J and m so how am I suppose to solve this?

 

[Doc Al]

Hint: Write an expression for J. (What force acts?)