An electric motor winds 200 turns of a thin coper wire on a unifrom of diameter 10 cm, in 2 seconds.then the length of the wire that is wound over the rod in one second is _______ m.

Options

A. 30
B. `10pi`
C. `20pi`
D. none of these

Answer

B

Explanation

Time taken to move along the steps ,
T= 8.5 s
As all the steps are identical , the distance travelled by the ant when it cilmbs one step
` (1/4 + 1//4) m = 1/2 m`
The total distance travelled = `(8 1//2 xx 1//2)` m
`= 17/ 2 xx 1/2 = 17/4` m
The total taken , (f) = 8.5 s
Average speed = `("total distance")/("total time") `
`(17/4)/(17/2 s) = 1/2 ms ^(-1) = 0.5 m s^(-1)`
Velocity = `("displacement")/("time")= (2.25)/(8.5) = 4.5/17 ms^(-1)`