A 0.4 kg ball thrown directly upward with an initial speed of 21 m/s reaches a m

Question

A 0.4 kg ball thrown directly upward with an initial speed of 21 m/s reaches a maximum height of 7.7 m. As the ball moves upward, the air exerts a drag force on the ball throughout the flight.

(a) When the ball travels from the release point to maximum height, does the mechanical energy of the ball-Earth system increase, decrease, or remain the same?

Increase

Remain the same

    Decrease

(b) What is the change in kinetic energy of the ball when it travels from the release point to maximum height?
J

(c) What is the change in potential energy of the ball-Earth system when the ball travels from the release point to maximum height?
J

(d) What is the work done by air resistance when the ball travels from the release point to maximum height?
J


(e) What is the average force due to air resistance?
N

(f) When the ball returns to the release point, its speed will be

Equal to 21 m/s

Less than 21 m/s

Greater than 21 m/s

Explanation / Answer

a) decreases due to air drag force

b) del K.E = 0.5*mv^2 = 0.5*0.4*21*21 = 88.2 J

c) del PE = mgh = 0.4*9.81*7.7 = 30.215 J

d) work done by air resistance = 88.2 - 30.215 = 57.985 J

e) F = 57.985 / 7.7 = 7.53 N

F) less than 21

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