Sarthaks Test
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in Laws of Motion and Friction by (274 points)
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A person of mass M kg is standing on a lift. If the lift moves vertically upwards according to given v-t graph then find out the weight of the man at the following instants :(g=10m/s). Find his apparent weight at t=12 seconds.

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From t=10 sec to t=12 sec

s = area under v-t graph

   = 1/2 * 4 * 20 = 40 mt

also s = ut + 1/2 at^2

from solving this you will get a = -5 m/s^2

So the lift is descending with a acc. = 5 m/s^2

So the forces on the person are g downwards ( w.r.t ground ) and a upwards  ( w.r.t ground ) so net force on person w.r.t ground is g - a = 10 - 5 = 5 m/s^2

Hence the apparent weight is W = m * a

= M * 5 = 5M

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