Terminal Velocity + Drag Force

[africanmasks]

Homework Statement

A sky diver of mass 79.5 kg jumps from a slow-moving aircraft and reaches a terminal speed of 53.0 m/s.

(a) What is the acceleration of the sky diver when her speed is 30.0 m/s?

What is the drag force on the diver when her speed is the following?
(b) 53.0 m/s (answer in N)
(c) 30.0 m/s (answer in N)

Homework Equations

The Attempt at a Solution

I found parts a and b (correct on Webassign), but I can't get part c.):

a.) a= 6.792 m/s2
b.) 779.1 N

Would part c.) just be: mg-ma?

(779.1)-(79.5)(6.792)
= 239.096 (WebAssign says it's incorrect)

 

[rl.bhat]

Drag force in air ia approximately proportional to v^2. So f = D*v^2.
Using the result from b, find D.
Use this value to solve c.

 

[africanmasks]

Thanks. I got it.

 

[Redbelly98]

Your answer looks good. Does WebAssign concern itself with doing significant figures properly?