n an experiment, a student places two carts on a level horizontal track with photogates X and Y that help the student determine the speeds of the carts, as shown above. The carts move toward each other with negligible friction. Cart A of mass m_A
m A
​
is moving to the right with speed v_A
v A
​
. Cart B of mass m_B\left(m_B>2m_A\right)
m B
​
(m B
​
>2m A
​
)
is moving to the left with speed v_B\left(v_B>3v_A\right)
v B
​
(v B
​
>3v A
​
)
. After passing through the photogates, the two carts collide. In a new experiment, a spring is attached to the right end of cart A. Cart B is at rest between the photogates when cart A is given an initial speed to the right, passes through photogate X, and collides with cart B. The speed of each cart before and after the collision is measured. It is discovered that the sum of the kinetic energies of the two carts after the collision is about 5% greater than the kinetic energy of cart A before the collision. Which of the following is the best explanation for the difference in the kinetic energy?
answer choices
The scale used to determine the masses of the carts is off by 5%.
During the collision, some of the kinetic energy of the carts is converted to heat.
Some of the elastic potential energy of the spring is converted to kinetic energy.
There is a small amount of friction between the track and the carts.
One end of the track is slightly higher than the other.