Force-Gravity Problem [Parachute & body]

[Spirit]

An 85 kg person is parachuting and experiencing a downward acceleration of 2.5 m/s2. The mass of the parachute is 4.8 kg.

What downward force is exerted by the person on the parachute?

>>What i am [was] thinking << ::
Well, i tried to solve it by using by using this method its wrong 'its online homework'

First, i assume that it should be Zero, since both are in the same system moving with the same accelaration, but it show wrong.

Then i try to solve by Total Force= Force of Gravity on the body + Force of Gravity on the Parachute + Force of Air (-) + Force of body on the parachute. and it did not help as well :( [the Air force is 655.54N as a correct answer]

Thank in advance for helping, i appreciate it.

 

[finchie_88]

All it is is that you have to look at the difference in the forces. The force acting down is 89.8g, and the force acting up must be 224.5N in order to get the acceleration of 2.5. The answer is just the difference between these two values.

 

[Spirit]

Unforutantly its not the correct answer,

This number as well is exactly the number of the air resistance, [upward]
So i tried to say the force is 0, by the person of the parachute. Still it won't work.

Any ideas? Thanks for the efforts :)

 

[HallsofIvy]

If there were no parachute what would the persons acceleration be?

The parachute is exerting force on the person to prevent him from falling at that acceleration. What difference in acceleration did the parachute produce? What (upward) force is the parachute exerting on him to produce that reduction in acceleration (F= ma)? Of course, he is exerting the same force (downward) on the parachute.