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# A boy standing on a weighing machine observe his weight to be $200 N$. when he suddenly jumps upwards, his friend notice that the reading increased to $400 N$. The acceleration with which the boy jumped will be

$(a)\;9.8 m/s^2\quad (b)\;29.4 m/s ^2 \quad (c)\;4.9 m/s^2 \quad(d)\;14.7 m/s ^2$

Force causing the acceleration
$400-200=200N$
mass of body $=\large\frac{200}{9.8}$
hence acceleration $=\large\frac{F}{m}=\large\frac{200}{\Large\frac{200}{9.8}}$
$\qquad=9.8 m/s^2$
Hence a is the correct answer.

edited Jan 26, 2014 by meena.p