C. the hockey puck will accelerate and continue moving in a straight line
Since the basketball and the tennis ball both travel to the same direction relative to the ground, the velocity of the basketball relative to the tennis ball is therefore the difference of their velocities.
0.5 m/s - 0.25 m/s = 0.25 m/s
Thus, the basketball travel for 0.25 m/s relative to the tennis ball.
Explanation:
The Coulomb's law states that the magnitude of each of the electric forces between two point-at-rest charges is directly proportional to the product of the magnitude of both charges and inversely proportional to the square of the distance that separates them:

In this case we have an electron (-e) and a proton (e), so:

In this case, the electric force is negative, therefore, the force is repulsive and its magnitude is:

Answer:
The atoms that contain an unstable combination of neutrons and protons, or excess energy in their nucleus