Newton's Laws Test Review Flashcards

Newton's Laws Test Review

To be properly prepared for this test, you should be able to:

• State each of Newton's three laws of motion.
• Use Newton's Laws to solve for Force, mass, or acceleration.
• Answer multiple-choice questions about applying Newton's Laws.

Key Concepts

The key to answering problems about force and motion is to understand and always keep in mind Newton's important discoveries:

• Newton's 1st Law: An object at rest remains at rest, and an object in motion remains in motion unless acted upon by an unbalanced force.
• Newton's 2nd Law: Mathematical model: F = ma. The larger the unbalanced force applied to an object, the greater the object's acceleration. The greater the mass of an object, the harder you must push or pull the mass to make it accelerate.
• Newton's 3rd Law: For every force, there is an equal and opposite force. Or, for every action, there is an equal and opposite reaction. Simply put, you can't touch something without it touching you back.

Acceleration

• An object is accelerating if and only if it is changing velocity.
• Changing velocity includes speeding up, slowing down, and changing direction.
• An object moving at a constant velocity is not accelerating. This means that an object can change its position (be in motion) and not be accelerating.
  • Example: A race car speeding down the straightaway of a racetrack at a constant velocity of 300 km/hour is not accelerating.

Balanced Forces

• If forces applied to an object are balanced, the object will not accelerate.
• If an object is not accelerating (speeding up, slowing down, or changing direction), then all forces on the object are balanced.
• Balanced forces cancel each other out.
  • Example: If two people pull on the ends of a rope in opposite directions with the same amount of force, the rope and the people will not accelerate.

Unbalanced Forces

• If the forces on an object are unbalanced, a net force results.
• A net force causes an object to accelerate in the direction of the net force.
• Objects always accelerate in the direction of the net force.
• If a net force is pushing/pulling you to the right, then you will accelerate toward the right. If a net force is pushing/pulling you to the left, then you will accelerate toward the left.
  • Example: If two people pull on the ends of a rope in opposite directions with different forces, then the rope will accelerate in the direction of the net force.

Acceleration (Continued)

• Some people think of acceleration as only speeding up. However, slowing down (changing speed) is also an example of acceleration.
• Mathematically, slowing down is expressed as a negative (-) acceleration.
• Speeding up is represented mathematically as a positive (+) acceleration.
  • Example: The acceleration of a car is positive when the driver "steps on the gas" to speed up, and acceleration is negative when they step on the brake to slow down.

Sample Test Questions

The following problems are the types of problems you'll be expected to know for the test. Read the questions and multiple choices carefully to select the best response(s) available.

1. Which one of the following is NOT consistent with a car that is accelerating?

   • a. The car is moving with an increasing speed.
   • b. The car is moving with a decreasing speed.
   • c. The car is moving at a high speed.

2. A football player is running down the football field in a straight line. He starts at the 0-yard line at 0 seconds. At 1 second, he is on the 10-yard line; at 2 seconds, he is on the 20-yard line; at 3 seconds, he is on the 30-yard line; and at 4 seconds, he is on the 40-yard line. This is evidence that:

   • a. he is accelerating
   • b. he is running at 5 yard/second
   • c. he is moving with a constant speed (on average)
   • d. he is changing direction

3. What is the acceleration of a car that maintains a constant velocity of 100 km/hr for 10 seconds?

   • a. 0
   • b. 10 km/hr/s
   • c. 10 km/s²
   • d. 1000 km/hr/s

4. Renatta Oyle is found driving her '86 Ford down Main St., leaving the following trail of oil drops on the pavement. Assume the drops of oil drip at a constant rate.

   If her car is moving from right to left, then:

   • a. her velocity has a rightward direction and her acceleration has a rightward direction.
   • b. her velocity has a rightward direction and her acceleration has a leftward direction.
   • c. her velocity has a leftward direction and her acceleration has a rightward direction.
   • d. her velocity has a leftward direction and her acceleration has a leftward direction.

5. Which of the following objects have momentum? Circle all that apply. Remember momentum = mass x velocity, p=mv.

   • a. A dog running down a hill
   • b. a UPS truck stopped in front of the school building
   • c. a merry-go-round spinning in place
   • d. a flea moving with constant speed
   • e. Scarsdale Middle School

6. A freight train (large mass) rolls along a track with considerable momentum, p=mv. If the train rolls at the same velocity but has twice as much mass when loaded with freight, its momentum when loaded is:

   • a. zero
   • b. quadrupled
   • c. doubled
   • d. unchanged

Velocity vs. Time Graph Questions

For the next several questions, consider the velocity vs. time graph below for the motion of an athlete running through an obstacle course from left to right. The motion is divided into several time intervals, each labeled with a letter.

[Velocity vs. Time Graph Description]

7. Which one(s) of the following force diagrams depict an object accelerating to the right? Circle all that apply.
8. A soccer player places a soccer ball at rest in front of the goal, lines up her shot, runs up on the ball, and kicks the ball as hard as she can. During the contact of her leg with the soccer ball, the force of her leg on the ball is the force of the ball on her leg.
   • a. Greater than
   • b. less than
   • c. equal to
9. If car A passes car B while both travel the same direction on the Interstate, then car A must be:
   • a. accelerating at a greater rate than car B
   • b. moving faster than car B and accelerating more than car B
   • c. moving faster than car B, but not necessarily accelerating
   • d. accelerating
10. During which time interval(s), if any, are the forces acting upon the athlete balanced? List all that apply.
11. During which time interval(s), if any, is a net force acting upon the athlete? List all that apply.
12. During which time interval(s), if any, is the net force acting upon the athlete directed toward the right (toward the finish line)? List all that apply.
13. During which time interval(s), if any, is the net force acting upon the athlete directed toward the left (toward the starting line)? List all that apply.
14. Which of the following statements are true of the concept of force? Circle all that apply.
    • a. One large football player tackles another smaller football player by running into him. While the smaller player is being tackled, he does not place a force upon the larger player.
    • b. A larger force is required to accelerate a 10kg rock than is required to accelerate a 5kg rock.
    • c. Forces always cause objects to accelerate.
    • d. An object can experience two or more forces and not accelerate.

Force Formula

15. What is the formula for force? How would you change it to find mass and acceleration?

• F = m \times a
• M = \frac{F}{a}
• a = \frac{F}{m}

15. A 35 kg body has an acceleration of 7 m/s². Find the net force acting on the body.

• F = m \times a
• F = 35kg \times 7m/s^2
• F = 245 N

15. A force of 70 N is acting on an object with an acceleration of 10 m/s². Find the mass of the object.

• M = \frac{F}{a}
• M = \frac{70N}{10m/s^2}
• M = 7 kg

15. A force of 2,000 Newtons is applied to a 1,000 kg car at rest. What is its acceleration?

• a = \frac{F}{m}
• a = \frac{2000 N}{1000 kg}
• a = 2 m/s^2

15. If the force acting upon an object is increased, what happens to the object's acceleration?

• It will increase.

15. In terms of motion, explain the difference between balanced and unbalanced forces acting on an object.

• Balanced forces mean no motion. Unbalanced forces mean there will be a change in motion.

15. Which force is pulling down constantly?

• Gravity