A 76.0 kg man stands on a spring scale in an elevator. Starting from rest, the e

Question

A 76.0 kg man stands on a spring scale in an elevator. Starting from rest, the elevator ascends, attaining its maximum speed of 1.19 m/s in 0.800 s. It travels with this constant speed for the next 5.00 s. The elevator then undergoes a uniform acceleration in the negative y direction for 1.90 s and comes to rest.
(a) What does the spring scale register before the elevator starts to move?
N

(b) What does it register during the first 0.800 s?
N

(c) What does it register while the elevator is traveling at constant speed?
N

(d) What does it register during the time it is slowing down?
N

Explanation / Answer

a .

N= mg = 76 * 9.8 = 744.8 N ;

b.

v= u + at

1.19= 0 + a * 0.8

a = 1.4875 m /s^2 ;

N - mg = ma ;

N = m ( g + a )

N = 76 ( 9.8 + 1.4875 )

N = 857.8 N

c .

constant speed , a= 0

N = m ( g + a )

N = 76 ( 9.8 + 0 )= 744.8 N

d .

v = u + at ;

0 = 1.19 + a * 1.9

a = -0.6262 m /s^2

N = m ( g - 0.6263 )

N = 76 (9.8 - 0.6263 )

N = 697.2 N <------ans

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