Question

1. when a rifle is fired, how does the size of the force of the rifle on the bullet compare to the force of the bullet on the rifle?

→how do the accelerations of the rifle and bullet compare? why?

Explanation:

According to Newton's third law of motion, when two objects interact, the forces they exert on each other are equal in magnitude and opposite in direction. So, the force of the rifle on the bullet and the force of the bullet on the rifle are equal in size.

For the accelerations, from Newton's second law \(F = ma\) (where \(F\) is force, \(m\) is mass, and \(a\) is acceleration), if \(F\) is the same (as per the third - law force pair) and the mass of the rifle (\(m_{rifle}\)) is much larger than the mass of the bullet (\(m_{bullet}\), \(m_{rifle}\gg m_{bullet}\)), then \(a=\frac{F}{m}\). So, \(a_{bullet}=\frac{F}{m_{bullet}}\) and \(a_{rifle}=\frac{F}{m_{rifle}}\), and \(a_{bullet}\gg a_{rifle}\)

Answer:

• The force of the rifle on the bullet is equal in size to the force of the bullet on the rifle.
• The acceleration of the bullet is much larger than the acceleration of the rifle. Because from \(F = ma\), when \(F\) (the magnitude of the force pair from Newton's third law) is the same and \(m_{bullet}\ll m_{rifle}\), \(a=\frac{F}{m}\) implies \(a_{bullet}\gg a_{rifle}\)