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What is the passenger's apparent weight?

The figure shows the velocity graph of a 75 kg passenger in an elevator.

http://img515.imageshack.us/img515/8872/picture1yd...

What is the passenger's apparent weight at t=1s? At t=5s? At t=9s?

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Let:

a be the acceleration of the lift,

g be the acceleration due to gravity,

m be the mass of the passenger,

R be the reaction of the lift floor on the passenger. This is his apparent weight.

From the graph:

At t = 1 sec, a = 4 m/s^2.

At t = 5 sec, a = 0.

At t = 9 sec, a = - 2 m/s^2.

(a) Lift ascending.

R - mg = ma

R = m(g + a)

= 75(9.81 + a) with a = 4, 0, - 2

= 1040 N, 736 N, 586 N.

(b) Lift descending.

mg - R = ma

R = m(g - a)

= 75(9.81 - a)

= 436 N, 736 N, 886 N.

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