I CANT COUNT FOR MY LIFE

Suppose that 27 j of work is needed to stretch a spring from its natural length of 6 m to a length of 9 m. (a) how much work is needed to stretch the spring from 12 m to 14 m? j (b) how far beyond its natural length will a force of 78 n keep the spring stretched?

The frequency of the fundamental of the guitar string is 320 hz. at what speed v do waves move along that string?

What is friction? how does it affect the motion of an object?