What is v a and v b and m a in Physics?

Shelly experiences a backward jolt when the driver starts the school bus. which of the following explains this phenomenon? a. the inertia of shelly b. the inertia of the bus c. the normal force of the seats on shelly d. the net force acting on shelly in a backward direction e. a zero net force acting on shelly

If we relied solely on the nonrenewable resources found in the u. s., which one would we run out of first at current usage levels? a. natural gas b. oil c. uranium d. coal

This is the number of complete movements of a wave per second.