A high diver of mass 55.0 kg steps off a board 10.0 m above the water and falls

Question

A high diver of mass 55.0 kg steps off a board 10.0 m above the water and falls vertical to the water starting from rest. If her downward motion is stopped 1.80 s after her feet first touch the water, what average upward did the water on her? A 82-kg man stands on a spring scale in an elevator. Starting from rest, the elevator seconds, attaining Rs maximum speed of 1.2 m/s in .73 s. The elevator travels with this constant speed for 5.0 s, undergoes a uniform negative acceleration for 1.7 s_r and then comes to rest. What does the spring scale register in each of the following time intervals? Before the elevator starts to move during the first 0.73 s of the elevator's ascent while the elevator's is travelling at constant speed during the elevator's negative acceleration

Explanation / Answer

A man weights 82 kg (force) therefore his mass is 82/9.81 kg, where g = 9.81 m/s^2 is gravitational constant.
a. at rest the scale shows man's weight 82 kg.
b. Elevator accelerates with constant acceleration a = 1.2/.73 m/s^2 and man's acceleration force ma adds to the gravitational force. Therefore scale will show: mg + ma = 82*(1 + a/g) = 95.75 kg.
c. There is no additional acceleration therefore scale show only gravitational weight 82 kg.
d. Elevator undergoes uniform deceleration a = 1.2/1.7 m/s^2 that subtracts from the gravitational force. Therefore the scale will show mg - ma = 82*(1 - a/g) = 76.09 kg.

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