A man throws a ball of $500 g$ in vertically upwards direction with a speed of $10 m / s$ . Calculate the amount of work done by force of gravity in $1 s e c o n d$ .

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Solution

Step 1: Given Data
Mass (m) $= 500 g$
Speed (u) $= 10 m / s$
Time (t) $= 1 s$
Step 2: Formula used
$F o r c e (F) = M a s s (m) x A c c e l e r a t i o n d u e t o g r a v i t y (g)$
$D i s p l a c e m e n t (s) = u t + \frac{1}{2} a t^{2}$
where u = speed; a = acceleration.
$W o r k d o n e (W) = F o r c e (F) x D i s p l a c e m e n t (s)$
Step 3: Converting the given mass into SI unit and calculating force
$m = 500 g = \frac{500}{1000} = 0.5 k g$
Take acceleration due to gravity (g) $= 10 m s^{- 2}$
$F = m x g F = 0.5 x 10 F = 5 N$
Step 4: Calculating displacement
Here $a = - g a s m o t i o n i s u p w a r d s o g r a v i t y w i l l b e n e g a t i v e$
$s = (10 x 1) + \frac{1}{2} (- 10) (1^{2})$
$s = 10 - 5 s = 5 m$
Step 5: Calculating work done
$W = F x s x \cos θ W = 5 N x 5 m x \cos 180 ° W = 25 x (- 1) W = - 25 J$
Hence, the amount of work done by force of gravity is $25 J$ .

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