Chapter 5
4. State Newton's third law of motion.
His third law states that for every action (force) in nature there is an equal and opposite reaction. In other words, if object A exerts a force on object B, then object B also exerts an equal and opposite force on object A.
39. Consider a baseball player batting a ball. Identify the action-reaction pairs (a) when the ball is being hit and (b) while the ball is in flight.
(a) Action; bat hits ball. Reaction; ball hits bat. (b) While in flight there are two interactions, one with the Earth's gravity and the other with the air. Action: Earth pulls down on ball (weight). Reaction: ball pulls up on Earth. And, action: air pushes ball, and reaction: ball pushes air.
76. Two 100N weights are attached to a spring scale as shown. Does the scale read 0, 100 N, or 200 N, or does it give some other reading? (Hint: Would the reading be different if one of the ropes were tied to the wall instead of to the hanging 100N weight?)
100N, the same reading it would have if one of the ends were tied to a wall instead of tied to the 100N hanging weight. Although the net force on the system is zero, the tension in the rope within the system is 100N, as shown on the scale reading.
27. A boxer punches a sheet of paper in midair and brings it from rest up to a speed of 25 m/s in 0.05 s. (a) What acceleration is imparted to the paper? (b) If the mass of the paper is 0.003 kg, what force does the boxer exert on it? (c) How much force does the paper exert on the boxer?
650 m/s^2
34. For each of the following interactions, identify action and reaction forces: (a) A hammer hits a nail. (b) Earth gravity pulls down on a book. (c) A helicopter blade pushes air downward.
A) A-the hammer hits the nail. R-the nail exerts an equal but opposite force on the hammer. B)A-The earth's gravity pulls down on a book, R-the book pulls up on earth. C) A-a helicopter blade pushes air downward, R-the air pushes up on the helicopter with an equal but opposite force.
51. If a Mack truck and Honda Civic have a head on collision, upon which vehicle is the impact force greater? Which vehicle experiences the greater deceleration? Explain your answers.
Both vehicles will feel the same force due to Newton's third law. Due to the smaller mass of the Honda Civic, the acceleration (deceleration) for the car will be greater than that for the more massive truck
11. If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?
Remember F = ma, and note that the cannon has a much greater mass than the cannon ball, so the cannon accelerates less for the same force.
79. A farmer urges his horse to pull a wagon. The horse refuses, saying that to try would be futile because it would flout Newton's third law. The horse concludes that she can't exert a greater force on the wagon than the wagon exerts on her and, therefore, that she won't be able to accelerate the wagon. Discuss your reasoning to convince the horse to pull
The Net Force of the horse will cause it to accelerate, because the horse is an external force.
12. Identify the force that propels a rocket.
The force that propels a rocket is the reaction to the force the rocket exerts on the exhaust gases.
10. Earth pulls down on you with a gravitational force that you call your weight. Do you pull up on Earth with the same amount of force
Yes, you pull up on Earth with the same force.
14. Can you physically touch a person without that person touching you with the same amount of force?
no you both would be touching each other with the same force
5. Consider hitting a baseball with a bat. If we call the force on the bat against the ball the action force, identify the reaction force.
the bat hitting the baseball