What does velocity mean in physics and what is it used for?

The image shows a pendulum in simple harmonic motion the pendulum starts at a and swing to e

Unpolarized light whose intensity is 1.19 w/ is incident on a polarizer. (a) what is the intensity of the light leaving the polarizer? (b) if the analyzer is set at an angle of = 41.0∘ with respect to the polarizer, what is the intensity of the light that reaches the photocell?

Explain why electric current cannot exist if a current doesn't have a voltage source.