Question

120.
A window is 50 cm long. A stone is falling
from a hight of 40 cm above the window. It
crosses the window in time of
1) 3/7 s
2) 2/7 s
3) 1/7 s
4) 4/7 s​

Answer 1

$\huge\color{blue}{\textbf{\textsf{QUESTION⇨}}}$

A window is 50 cm long. A stone is falling

from a hight of 40 cm above the window. It

crosses the window in time of

1) 3/7 s

2) 2/7 s

3) 1/7 s

4) 4/7 s

$\huge\color{blue}{\textbf{\textsf{ANSWER⇨}}}$

option 1 is correct

S1 = 50 cm

= 0.5 m

S2 = 40 cm

= 0.4 m

S = S1 + S2

= 0.4 + 0.5

= 0.9 m

= 9/10 m

a = 9.8 m/s^2

initial (u) = 0

Therefore from 2nd equation of motion :

s= ut+ ½ ×at2

9/10 = 0×t + ½ × 9.8 × t2

9/10 = 0+4.9×t2

t = √9/√49

t = 3/7 seconds