Question

A skydiver of mass 92 kg jumps from a slow-moving airplane and reaches a terminal speed of 49.9 m/s before opening her parachute.

(a) What was her acceleration when her speed was 36.9 m/s?

(b) What was the magnitude of the drag force at the same time?

Answer 1

Reference system.
Every vector (force, velocity or acceleration) that points upwards is considered positive and if it points downwards it is considered negative

the drag force is given by

where
is the density of the air
drag coefficient
effective area
the speed.

You can consider these elements as a cosntante K.

When the parachutist reaches its terminal velocity the drag force equals that of the weight, therefore

The value of the constant is

a.

the drag force is equal then to

considering that the drag force points up and the weight points down you get.

Second law of Newton.

evaluatin numerically

solution

The negative indicates that the acceleration points down

b.The magnitude of the drag force is

evaluating numerically wich

Solution