It is symbols to make it easier and to save space!
Explanation:
The darker the object, the better it emits heat, because it's a better absorber of light. On the other hand, a white object appears white because it reflects all the different wavelengths and absorbs little to no light.
Explanation:
It is given that,
Frequency of vibration, f = 215 Hz
Amplitude, A = 0.832 mm
(a) Let T is the period of this motion. It is given by the following relation as :



(b) Speed of sound in air, v = 343 m/s
It can be given by :




Hence, this is the required solution.