221 Chapter 7 Newton’s 3rd law examples
Example 1: (the horse that pulls Newton’s carriage)
A horse is supposed to bring Newton to the Royal Academy of Sciences. But it denies service with the
following argument: “I won’t pull. There’s no point. Newton’s 3rd law tells me that if I pull with 900N
then the carriage will pull back with an equal and opposite force. This means the forces cancel out, so
why should I pull?” Is the horse right?
Example 2
If you drop an apple which experiences a greater pull, Earth or the apple?
Which experiences a greater acceleration?
Example 3
The sled dog drags sleds A and B across the snow. The coefficient of friction between the sleds and the
snow is 0.10. If the tension in rope 1 is 150N, what is the tension in rope 2?
Example 4
The lower block in the figure is pulled on by a rope with a tension force of 20N. The coefficient of kinetic
friction between the lower block and the surface is 0.30. The coefficient of kinetic friction between the
lower block and the upper block is also 0.30. What is the acceleration of the 2.0 kg block?
Example 5 (at home)
Find the horizontal force F for which m1 does not slip either up or down along the wedge. No friction.
Example 6 (at home)
The two blocks are sliding down the incline. What is the tension in the massless string?
221 Chapter 7 Newton’s 3rd law examples
Example 1: (the horse that pulls Newton’s carriage)
A horse is supposed to bring Newton to the Royal Academy of Sciences. But it denies service with the
following argument: “I won’t pull. There’s no point. Newton’s 3rd law tells me that if I pull with 900N
then the carriage will pull back with an equal and opposite force. This means the forces cancel out, so
why should I pull?” Is the horse right?
Example 2
If you drop an apple which experiences a greater pull, Earth or the apple?
Which experiences a greater acceleration?
221 Chapter 7 Newton’s 3rd law examples
Example 3:
The sled dog drags sleds A and B across the snow. The coefficient of friction between the sleds and the
snow is 0.10. If the tension in rope 1 is 150N, what is the tension in rope 2?
221 Chapter 7 Newton’s 3rd law examples
Example 4:
The lower block in the figure is pulled on by a rope with a tension force of 20N. The coefficient of kinetic
friction between the lower block and the surface is 0.30. The coefficient of kinetic friction between the
lower block and the upper block is also 0.30. What is the acceleration of the 2.0 kg block?
221 Chapter 7 Newton’s 3rd law examples
Example 5:
Find the horizontal force F for which m1 does not slip either up or down along the wedge. No friction.
221 Chapter 7 Newton’s 3rd law examples
Example 6
The two blocks are sliding down the incline. What is the tension in the massless string?