Chapter 2 Review

Video Review

Key Concept Summary

TA Summary


Choose the law that you would use to analyze the motion in each scenario.

A boat glides through the water on a lake at constant speed in a straight line.
An airplane circles the airport at a constant speed while waiting to land.
A marathon runner begins running faster just before crossing the finish line.
Comparing the sizes of all forces that arise when a book sits on a table.
Describing the motion of a bench in the park.
An accelerating bullet causing the recoil of a gun.
A hot air balloon rising straight up at a constant speed.
A submarine falling straight towards the ocean bottom at a constant speed.
Comparing the forces on two boxers' gloves as they come in contact.


The laws of nature are treated differently for an object in uniform motion and an object at rest.
If an object changes its state of motion (i.e. its direction or speed) then it must be accelerating.
When an astronaut travels to the moon, his or her weight changes. Therefore, the astronaut's mass must also change.
For an object to change its state of motion, an unbalanced force must act on it.
Objects that interact always exert the same strength of force on one another.


Which of the following explanations correctly describes rocket propulsion? (You should find it helpful to know that rocket motors function perfectly well in the vacuum of space where there is no air.)
When a body is acted upon by a single constant unbalanced force,
If an object is moving in a straight line at a constant speed, which of the following must be true?

Free Response

  1. Restate Newton’s Laws in your own words.
  2. If velocity is zero, does acceleration have to be zero? If acceleration is zero, does velocity need to be zero? Give an example to illustrate your answers.
  3. If there is a constant net force on an object that starts out at rest, what happens to its speed?
  4. When you drive, the car engine generates a constant force as long as you give it a constant amount of gas. Why doesn’t your car accelerate at a constant rate like described in the previous question?
  5. Give an example of a situation where it is important to use Newton’s Third Law.
  6. A rubber chicken thrown into the road hits a car moving 60 mph. Justify your answers using Newton’s laws.
  7. Upon contact, does the car or the chicken experience the greater force?
  8. Does the car or the chicken experience the greatest acceleration?
  9. What two forces on Earth make Newton’s First Law difficult to see? How do they prevent most objects from traveling in uniform motion?
  10. How do force and mass affect acceleration?
  11. A semi-truck going 70 mph runs into a patch of black ice and glides across the ice. No unbalanced forces (such as friction) are present on the truck.
    • What type of motion does the truck experience after encountering the ice?
    • What law applies to the scenario?
    • If the patch of completely frictionless ice extended in front of the truck for six miles, what is the truck’s speed right before reaching the end of the ice patch?
  12. During a football game, a wide receiver who only weighs 160 lbs catches the football on a short curl route. From the receiver’s blind side, a 270-lb linebacker running full speed hits the receiver, causing the linebacker’s speed to slightly decrease and knocking the receiver into the stands.
    • What type of motion does the linebacker experience when hitting the receiver?
    • What type of motion does the receiver experience when hit by the linebacker?
    • Compare the accelerations of the two players. Use Newton’s 2nd and 3rd Laws to explain your answers.
  13. A rocket in space is burning its engines, creating a constant unbalanced force on it. The force is applied to the rocket indefinitely.
    • Describe the rocket’s motion. What will happen to the rocket’s speed?
    • Which of Newton’s laws apply to this scenario?
    • When the rocket runs out of fuel, what happens to its speed?
  14. Ethan pulls on a cart that his brother, Cameron, sits on. They both head straight home with progressively increasing speed. Analyze the motion of the cart by doing the following:
    • Describe the cart’s motion. Is it uniform or accelerated?
    • Identify which law(s) of motion apply.
    • Identify all forces that are acting on the cart and which forces influence the cart’s motion. A labeled diagram with arrows representing forces is often helpful here.
    • Compare the size of relevant forces. Are the forces balanced or unbalanced?
    • Use Newton’s Third Law to compare the size of the force Ethan exerts on the cart to the force the cart exerts on Ethan. Explain how the cart and Ethan can both be speeding up in the same direction, taking into account the Third Law.
    • If Cameron jumps out of the cart while Ethan keeps pulling with the same force, what will happen?
  15. In a car crash between a small car and an SUV, the occupants of the small car are much more likely to be injured. Use Newton’s Laws to explain why.
  16. Use Newton’s laws to explain how safety features in cars like seat belts, crumple- zones (places where the car’s frame is designed to bend in a crash), and air bags reduce the risk of injury in a crash.
  17. A boy is standing on a skateboard at rest. The boy jumps forward off the skateboard.
    • Which of Newton’s Laws apply to this situation?
    • What happens to the boy and to the skateboard?
    • What would happen if the boy jumped off sideways? Why are the situations different?