An ideal spring is used to fire a 15.0-g block horizontally. The spring has a spring constant of 20 N/m and is initially compressed by 7.0 cm. The kinetic energy of the pellet as it leaves the spring is:

Question

Quizplus · Accepted Answer

The potential energy stored in the compressed spring is:
$U_s = \frac{1}{2}kx^2 = \frac{1}{2}(20\ 	ext{N/m})(0.07\ 	ext{m})^2 = 0.049\ 	ext{J}$

This potential energy is converted entirely into kinetic energy as the block leaves the spring. Therefore, the kinetic energy of the block is also 0.049 J, which is equivalent to 4.9 J when rounded to one significant figure. Thus, the correct answer is C.

An Ideal Spring Is Used to Fire a 15