How Is the Vertical Force on a Sliding Fireman Calculated?

[Amelina Yoo]

Homework Statement

Fireman weighs 100kg. He slides down a vertical pole with acceleration 3.0ms^-2.

a) Magnitude and direction of vertical force exerted by the pole on fireman?

Homework Equations

f=ma

The Attempt at a Solution

f=ma
f=100(3.0)
f=300N vertically up.

But the answer says that it is actually 680N vertically up, and I do understand how they came to this conclusion.
Can you please explain where to go beyond this point? Or point out a mistake I may have made? Thank you.

 

[gneill]

The acceleration of a mass depends upon the net force acting on the mass. Draw a free body diagram and identify all the forces that are acting on the fireman. How do the acting forces combine to make up the net force?