A 55 kg skydiver drops out of a plane from an altitude of 40,000 m. Thanks to he

Question

A 55 kg skydiver drops out of a plane from an altitude of 40,000 m. Thanks to her parachute, her velocity when she reaches the ground is only 5 m/s. Determine the average magnitude of F_air resistance on the skydiver A 7 kg bowling ball with initial velocity of 8 m/s experiences friction (mu = .053) during its 18.3 m trip down the lane. Determine its velocity when it reaches the pins. Starting from rest, a 10 kg kid experiences a friction force of 6 N during the 10 m descent down a 3-m-tall playground slide. Determine the kid's velocity at the bottom of the slide.

Explanation / Answer

1. applying work energy theorem,

Work done by gravity + work done by air resistance = change in KE

m g h - Fres h = m (vf^2 - vi^2 ) / 2

(55 x 9.81 x 40,000) - (Fres x 40,000) = 55 ( 5^2 - 0 ) / 2

Fres = 539.53 N ........Ans

2. friction force , f = uk m g = 0.053m g

Applying work energy theorem,

work done by friction = change in KE

- (0.053 m g) (18.3) = m ( v^2 - 8^2) / 2

- 19.03 = v^2 - 8^2

v = 6.71 m/s

3. Work done by gravity + work done by friction = change in KE

(10 x 9.81 x 3) + ( - 6 x 10) = 10 v^2 /2 - 0

v = 6.85 m/s

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