IIT JEE , AIEEE Forum - Physics , Mechanics

deepali04

A chair is suspended from a spring with spring constant 600N/m . The periodic time for oscillation of this system is 1s . When a man sits in the chair ,the periodic time for oscillation becomes 2.5s . Theweight of man is?

punitcooldude

T =2

M/k

M = k/4

²

600/40

15kg
this is the mass of the chair
let mass of man be m kg
T

M

(m + 15)/15 = (2.5/1)²
m + 15 = 375/4
m = 78.75 kg
so, wt. = 787.5 N
rate the answer if its correct

iitkgp_bipin

Time period is given by T = 2

(m/k)

Let mass of chair be M.
1 = 2

(M/600)
M = 600/4

²

When a man of mass m sits on chair :
2.5 = 2

(M+m/k)
M+m = 600(2.5²/4

²)

Hence m = 600(2.5²/4

²) - 600/4

²

Approx. m = 78.75 kg
Weight = 787.5 N

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