Which of the following is true about a balance force? a) Results in no net movement
b) Causes an object to decelerates
c) Causes an object to speed up
d) The opposite forces acting on an object are unequal.

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?