Newton's fundamental laws

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Homework Statement


A parachutist of mass 70kg, in free fall at 136 km/h, opens a parachute. if the chute creates a 895 N air resistance force and the parachutist is being pulled down by a force of gravity at 686 N
a) find hte acceleration of the parachutist
b) how far does she fall in 5.0 s?

Homework Equations


Fnet = ma, d = v1t + 1/2at^2

The Attempt at a Solution


First i determined part A and i got the answer 3.0 m/s^2 [up]. which is correct in the answer key.
then i used the equation d = v1t + 1/2at^2, converting 136 km/h to m/s
d = v1t + 1/2at^2
d = 37.7 m/s(5s) + 1/2(3 m/s^2)[(5s)^2]

and i got 226.4 m. the correct answer is 150m. i dont know what i did wrong. i then tried using the acceleration due to gravity, 9.81 m/s^2 because it is a freefall but the answer was still wrong.
please help!!
 

Answers and Replies

  • #2
Doc Al
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The person's initial speed is downward, thus negative.
 

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