Answer:
F = 2520 N
Explanation:
We have,
The maximum acceleration of a fist in a karate punch is 4200 m/s². The mass of the fist is 0.6 kg.
It is required to find the force that the wood place on the fist. Force is given by the product of mass and its acceleration such that,
F = ma

So, the force of 2520 N is acting on the wood.
Newtons 3.law: Action = Reaction
If a body exerts a force on a rope of 400 N the rope exerts a force on the body of 400N also. So the tension in the rope is 400N. See pictures below.
I think the question meant to say net force on the box. Since force is a vector, the direction matters. 20N left is negated completely by the 50N right, which means the net force is 50N-20N to the right, 30N.
Answer:
Newton, absolute unit of force in the International System of Units (SI units), abbreviated N. It is defined as that force necessary to provide a mass of one kilogram with an acceleration of one metre per second per second.