Question

A very large number of balls are thrown vertically upwards in quick succession in such a way that the next
ball is thrown when the previous one is at the maximum height. If the maximum height is 5m, the number of
ball thrown per minute is (take g -10 ms?)
(a) 120
(b) 80
(c) 60
(d) 40​

Answer 1

Explanation:

given : distance =5m,a=g,

g=-10m/s

the motion is upward ,

by Newton second law

s=ut+ 1/2gt square

5=0+1/2-(10)t

5=5*t

t=5/5=1second

1s=60m

so 60 balls thrown

Answer 2

Answer:60 balls

Explanation:

Given

balls are thrown in succession such that another ball is thrown when first ball attains a maximum height of 5 m

let u be the initial velocity of ball thrown

$v^2-u^2=2as$

here a =g

s=5 m

$0-u^2=2\times 9.8\times 5$

u=9.899 m/s

time taken to reach max height

v=u+at

$0=9.89-9.8\times t$

$t=1.0101 s$

Thus  balls thrown in 1 minute is

$=\frac{60}{1.0101}=59.39 \approx 60 balls$