(i) A man is standing between two vertical walls 680 m apart . He claps his hands and hears two distinct echoes after 0.9 second and 1.1 second respectively. What is the speed of sound in the air? (ii) A door is pushed , at a point whose distance from the hinges is 90 cm , with a force of 40 N. Calculate the moment of the force about the hiages.

(i) A man is standing between two vertical walls 680 m apart . He clap

1.	(i) A man is standing between two vertical walls 680 m apart . He claps his hands and hears two distinct echoes after 0.9 second and 1.1 second respectively. What is the speed of sound in the air? (ii) A door is pushed , at a point whose distance from the hinges is 90 cm , with a force of 40 N. Calculate the moment of the force about the hiages.
Answer» SOLUTION :(i) Velocity = `("Distance travelled by sound")/("Time TAKES")` `v=(2D)/(t)` `d_1=(vt_1)/2 and d_2-(vt_2)/2` `d=V/2(t_1+t_2)` `v=(2d)/(t_1+t_2)` `=(2xx680)/(0.9+1.1)=(2xx680)/2=680"ms"^(-1)` `v = 680 "ms"^(-1)` (ii)The moment of a force M = `Fxxd` `d=90 cm = 0.9m` Hence, moment of the force `=40xx0.9=36` Nm