(i)A man is standing between two vertical wall 680 m apart. He claps his hands and hears two distinct echoes after 0.9 seconds and 1.1 seconds respectively .What is the speed of sound in the air ?
(ii) An electric heater of resistance 5`Omega` is connected to an electric source .If a current of 6 A flows through the heater then find the amount of heat produced in 5 minutes.

Explanation

`Velocity =("Distance travelled by sound")/("Time taken")`
`v=(2d)/(t)`
`d_1=(vt_1)/(2)& d_2=(vt_2)/(2)`
`d_2=(v)/(2)(t_1+t_2)`
`v=(2d)/((t_1+t_2))`
`=(2xx680)/((0.9+1.1))``v=680ms^(-1)`
(ii) Given resistance R=5 `Omega`,current I=6A
Time t=5 minutes =`5xx60s` =300s
Amount of heat produced, H=`I^(2)Rt`
`H=6^(2)xx5xx300`. Hence H=5400J