A tuning fork is vibrating. The displacement,ycentimetres, of the tip of one of the prongs from its rest position aftertseconds is given by

y= 0.1sin(100 000t)°

Find :

a. the greatest displacement and the time at which it first occurs,

b. the time taken for one complete oscillation of the prong,

c. the number of complete oscillations per second of the tip of the prong

I answered a. and b. correctly with the following responses:

a. y= 0.1 cm., t= 0.000 9 s.

b. 0.003 6 s.

For c. I answered 277 (complete oscillation p/s) taking the answer to b.

1/0.0036 = 277.8 (correct to 1 d.p.)

Which makes 277completeoscillations per second.

However the correct answer is given to be 278.

Why is this?