Answer: marble 4 (40g)
Explanation:
The kinetic energy of an object is given by:
[tex]E_k = \frac{1}{2}mv^2[/tex]
where
m is the mass of the object
v is its speed
In this problem, all the marbles have same speed (v=3 m/s), so their difference in kinetic energy depends on their different mass only. In particular, we see that the kinetic energy is proportional to the mass: therefore, the larger the mass, the more the kinetic energy.
For this reason, the ball with the greatest kinetic energy is marble 4, which has the greatest mass (40 g). Its kinetic energy is given by
[tex]E_k=\frac{1}{2}(0.04 kg)(3 m/s)^2=0.18 J[/tex]
