A cannon with a mass of 850 kg is stationary, and loaded with a 10 kg cannonball. Upon firing, the cannonball is moving at 93.5 m/s and the cannon is moving backwards at 1.1 m/s. What is the difference between the kinetic energy of the system before and after the explosion?

Newton's third law states that for every action there must be an equal and opposite reaction, so the forces on the cannon and cannonball are equal in magnitude (but not direction). and the mass of the cannon is larger than the mass of the cannonball, so the acceleration is lesser for the cannon than for the cannonball.

Explanation:

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

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im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.