#6 - Lower frequencies correspond to <em>longer</em> wavelengths.
#7 - To change the pitch of a sound, you have to change its <em>frequency</em>.
Answer:
Absence of light causes shadow
Explanation:
The shadow is of the black colour because it is formed by the white light from the sun. Black is the opposite colour of white. In case you use different colour of light to cast a shadow you will get a shadow of opposite colour of light used to cast shadow.
Explanation:
It is given that,
Mass of the ball, m = 0.06 kg
Initial speed of the ball, u = 50.4 m/s
Final speed of the ball, v = -37 m/s (As it returns)
(a) Let J is the magnitude of the impulse delivered to the ball by the racket. It can be calculated as the change in momentum as :

J = -5.24 kg-m/s
(b) Let W is the work done by the racket on the ball. It can be calculated as the change in kinetic energy of the object.


W = -35.1348 Joules
Hence, this is the required solution.