1.

The equation of a wave is given by y = 10 ((2 pi )/(45) t + alpha ) . If the displacement is 5 cm at t = 0 , then the total phase at t = 7.5 sec. is :

Answer»

`(pi)/(3)`
`(pi)/(2)`
`(pi)/(6)`
`pi` .

SOLUTION :y = 10 SIN `((2pi t)/(25) + a)`
at t = 0, y = 25 cm
`therefore ` 5 = 10 sin `(0 + alpha) rArr(1)/(2) = sin alpha`
`therefore alpha = 30^(@) or (pi)/(6)` radians.
Now att = 7.5s. Total phase is
`phi = (2pi xx 7.5)/(45) + (pi)/(6) `
`phi = (pi)/(3) + (pi)/(6)= (pi)/(2) `
So correct CHOICE is (b).


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