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Unit 01 Forces and the Laws of Motion
Problem Set 01
Part One: Concepts
1. Define: Force, Net Force
2. What are the three ways a net force an affect the motion of an object?
3. What is the SI unit of force? What are the fundamental units of force?
4. Why is force a vector?
5. A chair is pushed forward with a force of 185N. The gravitational force of Earth on the chair is 155N downward, and the floor exerts a force of 155N upward on the chair. Draw a free-body diagram showing the forces acting on the chair.
6. A physics book is at rest on a desk. Gravitational force pulls the book down. The desk exerts an upward force on the book that is equal in magnitude to the gravitational force. Draw a free-body diagram of the book.
7. Draw a free-body diagram of a football being kicked. Assume that the only forces acting on the ball are the force due to gravity and the force exerted by the kicker.
8. Draw a free-body diagram for each of the following objects (show size of force with big or small arrow):
a. A projectile accelerating downward in the presence of air resistance.
b. A crate being pushed across a flat surface at a constant speed.
9. Define Equilibrium.
10. Can an object be in equilibrium if only one force acts on the object?
11. If an object is at rest, can we conclude that no external forces are acting on it?
12. An 1850kg car is moving at a constant speed of 1.44m/s. What is the net force on the car?
13. If a car is traveling west with a constant velocity of 20m/s, what is the net force acting on the car?
14. If a car is accelerating downhill under a net force of 3674N, what additional force would cause the car to have a constant velocity?
15. Is it possible for an object to be in motion if no net force is acting on it? Explain.
16. An object thrown into the air stops at the highest point in its path. Is it in equilibrium at this point? Explain.
17. A large ball is placed on a bed of a truck but is not tied down.
a. Explain why it is wrong to say, “as the truck accelerates forward, the ball slides across the bed until it hits the tailgate.”
b. If the driver slammed on the brakes, what would happen to the ball?
18. A space explorer is moving through space far from any planet or star and notices a large rock, taken as a specimen from an alien planet floating around the cabin of the ship.
Should the explorer push it gently or kick it toward the storage compartment? Why?
19. Identify the action-reaction pairs in the following situations:
a. A person takes a step. b. A snowball hits someone in the back.
c. A baseball player catches a ball. d. A gust of wind strikes a window.
20. If a small sports car collides head-on with a massive truck, which vehicle experiences the greater impact force? Which vehicle experiences the greater acceleration? Explain.
21. Explain why a rope climber must pull downward on the rope in order to move upward.

Part Two: Constructing Responses
22. The force that attracts Earth to an object is equal to and opposite to the force that Earth exerts on the object. Explain (in a 3-step AES) why Earths’ acceleration is not equal to and opposite the object’s acceleration?
23. When a tablecloth is pulled out from underneath a cup and plate, the cup and plate stay on the table. Why? Explain (in a 3-step AES) why this is using Newton’s 1st Law of Motion.

Part Three: Easy Problem Solving
24. What is the net force on a stapler if Ms Bucci pulls it with a force of 35N to the left and John pulled it 12N to the right? Which way did the stapler go?
25. In a tug of war competition, Sally pulled 30N east along with Bobby who pulled 13N east. If their opponent Tyler pulled with a force of 20N and Jason 23N west, who team won?
26. A row boat is being propelled with a force of 450N north by the rowers, but the water current pushes south on the boat with a force of 230N. If the wind also pushes north with a force of 100N, find the net force (including direction) on the boat.
27. A broken down car has a mass of 1500kg and is accelerated at a rate of 1.5m/s2 by several people pushing. With what force do the people push the car?
28. A 6.0kg object undergoes an acceleration of 2.0m/s2. What is the magnitude of the net force acting on the object?
29. The net force on the propeller of a 3.2kg model airplane is 7.0N forward. What is the acceleration of the airplane?
30. A soccer ball kicked with a force of 13.5N accelerates at 6.5m/s2 to the right. What is the mass of the ball?
31. The net force on a golf cart is 390N north. If the cart has a total mass of 270kg, what are the magnitude and direction of the cart’s acceleration?
32. A car has a mass of 1.50x103kg. If the force acting on the car is 6.75x103N to the east, what is the car’s acceleration?
33. A bag of sugar has a mass of 2.26kg. Determine its mass and weight on…
a) …on Earth b) …on the moon c) …on Jupiter (g=-25.9m/s2)
34. A 3.46kg briefcase is sitting at rest on a flat floor.
a. What is the briefcase’s net acceleration? b. What is its weight in Newtons?

Part Four: Medium Problem Solving
35. Two forces are applied in the same direction to a car in an effort to accelerate it, F1=235N, F2=301N
a. What is the resultant of these two forces?
b. If the car has a mass of 3200kg, what acceleration does it have?
36. Due to the airplanes engines a 4000kg airplane is pushed forward with a force of 70000N, if the wind pushes back on the plane with a force of 25000N, what is the net acceleration of the plane?
37. What is the mass of a sailboat which is accelerating at 13m/s2 that is pushed by the wind with a force of 140N and the current of water in the same direction with a force of 210N?
38. What is the acceleration of a 65kg boy and bicycle which is pedaled with a force of 100N, and overcomes a frictional force of 25N? (friction is always in the opposite direction of the motion)
39. A 5.0kg bucket of water is raised from a well by a rope. If the upward acceleration of the bucket is 3.0m/s2, find the force exerted by the rope on the bucket of water? (You must consider gravity in this!)

Part Five: Hard Problem Solving
40. The forces acting on a sailboat are 390N north and 180N east. If the boat has a mass of 270kg, what are the magnitude and direction of the boat’s acceleration?
41. Four forces act on a 400kg hot-air balloon, shown here.
Find the magnitude and direction of the resultant acceleration on the balloon.

Part Six: Difficult Problem Solving
42. Kathy and Jim are pulling a box of physics equipment with an acceleration of 0.56m/s2. If they are pulling with a force of 120N 20o above the horizontal, what is the mass of the box?
43. A 50kg box is pulled by Ms Bucci with a force of 320N at an angle of 25o above the horizontal. What is the acceleration of the box?