Question

A) An 80- kg man stands in an elevator. What force does he exert on the floor of the elevator under the following conditions? The elevator is stationary.

B) The elevator accelerates upward at 2.2 m/s2.

C) The elevator rises with constant velocity of 4.5 m/s.

D) While going up, the elevator accelerates downward at 1.8 m/s2. The elevator goes down with constant velocity of 7.2 m/s.

Answer 1

A)

elevator is stationary

acceleration a = 0

along vertical

Fnet = m*a = 0

N - W = 0

N = W = m*g = 80*9.8 = 784 newtons

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B)

elevator is accelerating up with a = +2.2 m/s^2

acceleration a = + 2.2 m/s^2

along vertical

Fnet = m*a

N - W = m*a

N = W + m*a

N = 80*9.8 + 80*2.2 = 960 newtons

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C)

elevator rise with constant velocity

acceleration a = 0

along vertical

Fnet = m*a = 0

N - W = 0

N = W

N = 80*9.8 = 784 newtons

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(D)

elevator is accelerating up with a = +2.2 m/s^2

acceleration a = - 1.8 m/s^2

along vertical

Fnet = m*a

N - W = m*a

N = W + m*a

N = 80*9.8 - 80*1.8 = 640 newtons

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elevator goes down with constant velocity

acceleration a = 0

along vertical

Fnet = m*a = 0

N - W = 0

N = W

N = 80*9.8 = 784 newtons