Applications Of Newton's Third Law
Helena Dedic
Beware: Many of the solutions to these exercises use !
Exercise 1
A 0.3 kg puck slides on the ice which exerts a 0.06 N force of friction on it. What are all the action-reaction pairs of the puck sliding on the ice?
Exercise 2
A 70 kg man pulls a rope attached to a 100 kg box with a horizontal force of 200 N as shown. The box doesn't move.
(a) Calculate all the forces exerted on the box.
(b) Calculate all the forces exerted on the man.
Exercise 3
The same 70 kg man pushes down at an angle of 30° to the horizontal with the force of 200 N on the 100 kg box. The box still doesn't move.
(a) Calculate all the forces exerted on the box.
(b) Calculate all the forces exerted on the man.
Exercise 4
Bob and Jim are involved in a fight and they push each other. Jim's mass is 50 kg and Bob's mass is 120 kg. The maximum friction between the horizontal surface and Jim's feet is 250 N. Similarly, the maximum friction between the horizontal surface and Bob's feet is 600 N. State which of the following statements are incorrect and why, and also state which of the following statements are correct and why:
(a) The force exerted on Jim by Bob is larger than the force with which Jim pushes Bob.
(b) The force of friction exerted on Bob is always larger than the force of friction exerted on Jim.
(c) The force with which Jim pushes Bob is the same as the force with which Bob pushes Jim.
(d) Bob is at rest because the force exerted by Jim on Bob is balanced out by the force that Bob exerts on Jim.
(e) Jim may be at rest because the force of friction cancels out the force exerted by Bob.