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Force and Motion Study Guide Answer Key

1. What is the unit of the following terms?

a. Weight- Newton

b. Length- Kilometer

c. Mass- Kilogram

d. Force- Newton

2. In each of the following illustrations, give is the net force (Include if it is balance or unbalance and the direction)

[pic] unbalanced, left

[pic] balanced

[pic] [pic] [pic] unbalanced, right

3. What is inertia? The resistance of an object to change

4. Inertia is known as which Newton’s law of Motion? 1st law

5. What is the relationship between mass and inertia? The greater the mass, the greater the inertia

6. Which of the following will have the greatest inertia? Explain why?

[pic] Ball 3 has a greater mass, therefore it has a greater inertia.

7. How does friction affects motion? Friction slows down the motion of an object.

8. How does gravity affects motion? Gravity pulls an object downward.

9. What happens to a moving toy car if there were no forces to act on it? According to Newton’s 1st law of motion, the toy car will continue on indefinitely unless acted upon by an outside force.

10. What is required for a car to increase its acceleration? 1. You can make sure that the velocity and acceleration are in the same direction. 2. Increase the force on the car. 3. Make the car lighter.

11. If a ball is on the hood of a truck going 40 mph, what would happen to the ball and its speed if the truck comes to a complete stop. According to Newton’s 1st law of motion, the ball would keep moving forward at the same speed.

12. Calculate the speed for the following problem: A motorcycle traveling the distance of 400 meters in 16 seconds is traveling at what speed? (Show all work and use correct units of measurement.)

s = d/t

= 400/16

= 25 m/s

13. A change in motion can be a change in an object’s _position____, _speed______, or _acceleration__.

14. This test paper is sitting at rest on your desk. Which of the following statements best describes this situation?

a. There are no forces acting on your paper.

b. Your paper pushes on the desk only.

c. The desk pushes on your paper only

d. The forces acting on the paper are balanced.

15. What forces are acting on a dropped book that falls to the floor?

a. Gravity only

b. Gravity and air resistance

c. Air resistance

d. Friction only

16. Which one of the following objects has the greatest inertia?

a. ping pong ball b. a golf ball c. a soft ball d. a bowling ball

17. A falling object is pulled down by the earth. The earth is pulled up toward the object. Why doesn’t the earth move?

a. Only the earth has gravity.

b. The Earth has a very large mass and a small acceleration.

c. The Earth has a very small mass and a large acceleration.

d. Air resistance gets in the way.

18. When you walk across the ground and push on it with your feet...

a. There is no effect on the ground.

b. The ground pushes back less strongly than your feet.

c. The ground pushes back more strongly than your feet.

d. The ground pushes back on your feet with equal force.

19. Which of Newton's Laws is being described as a rocket is lifting off the ground? 3rd law

[pic]

20. In the diagram above, which graph best matches a person sitting on a bench and waiting? A

21. Which graph best matches a person walking away slowing and returning quickly? D

22. A duck flies 60 meters in 10 seconds. What is the duck’s speed?

s = d/t

= 60/10

= 6 m/s

23. List the four types of friction and give an example of each.

Rolling friction – tires on a car moving

Sliding friction – pushing a box across the floor

Fluid friction – swimming or a kite flying through the air

Static friction – an SUV sitting in the garage

24. I pull a cart with boxes across the floor. The surface changes from carpet to tile. Why do I have to pull/push harder on the carpet to move the same cart? There is more friction between the boxes and the carpet than there is between the boxes and the tile because the tile is smoother.

25. A change in direction or speed is known as _acceleration_.

26. Which of Newton’s 3 Laws of Motion explains why objects with mass don’t just start moving by themselves? 1st law

27. If I want to accelerate an object with twice as much mass as another object, what do I have to do? Increase the net force

28. If all the forces are in balance, what will the motion of an object be? There is no motion.

29. What is the difference between speed and velocity? Velocity is speed in a given direction.

30. What are net forces? All of the forces acting on an object

31. Explain the difference between balanced and unbalanced forces.

Balanced forces equal zero, therefore, there is no movement. Unbalanced forces will cause an object to move and/or change direction.

32. What is friction? Friction is the contact force that acts in the opposite direction of an object’s movement.

33. State Newton’s 3 laws of motion and give a real life example of each.

1st law – an object at rest will stay at rest unless an outside force acts on it; an object in motion will remain in motion unless an outside force acts on it – a book lying on a shelf will not move until someone picks it up or the cat knocks it down, and a ball hit in the air by a batter will not stop until someone catches it, fluid friction slows it down and gravity pulls it down.

2nd law – force equals mass times acceleration – an empty shopping cart requires less force to move it around the grocery store than a full shopping cart.

3rd law – for every action, there is an equal but opposite reaction – a fish uses its fins to push water back and the water pushes the fish forward with an equal force.

34. Label the examples below as an example of speed, velocity, or acceleration.

a. A snail moves 0.013 meters in 1 second. speed

b. Geese fly about 64 kilometers per hour when they migrate south. velocity

c. A train slows to a stop at a station. acceleration

35. Formula: F= ma (Force = Mass x Acceleration) A racing car has a mass of 950 kg. It undergoes an acceleration of 3.00 m/s. What is the net force acting on the car?

F = ma

= 950 x 3

= 2850 N

36. You arrive in my class 45 seconds after leaving math which is 90 meters away. How fast did you travel?

s = d/t

= 90/45

= 2 m/s

37. Acceleration = Vf - Vi / t (Acceleration = Final Velocity- Initial Velocity / Time) A car starts from rest and accelerates uniformly over a time of 5.21 seconds for a distance of 110 meters. Determine the acceleration of the car.

Vf - Vi

t

= 110 - 0

5.21

= 21.1 m/s2

38. Which of the two vehicles would be hardest to accelerate, a motorcycle or an 18-wheeler? Explain why. An 18-wheeler because it has more mass.

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