Ch 04: Intro to Forces (Dynamics)See all chapters
All Chapters
Ch 01: Units & Vectors
Ch 02: 1D Motion (Kinematics)
Ch 03: 2D Motion (Projectile Motion)
Ch 04: Intro to Forces (Dynamics)
Ch 05: Friction, Inclines, Systems
Ch 06: Centripetal Forces & Gravitation
Ch 07: Work & Energy
Ch 08: Conservation of Energy
Ch 09: Momentum & Impulse
Ch 10: Rotational Kinematics
Ch 11: Rotational Inertia & Energy
Ch 12: Torque & Rotational Dynamics
Ch 13: Rotational Equilibrium
Ch 14: Angular Momentum
Ch 15: Periodic Motion (Oscillations)
Ch 16: Waves & Sound
Ch 17: Fluid Mechanics
Ch 18: Heat and Temperature
Ch 19: Kinetic Theory of Ideal Gasses
Ch 20: The First Law of Thermodynamics
Ch 21: The Second Law of Thermodynamics
Ch 22: Electric Force & Field; Gauss' Law
Ch 23: Electric Potential
Ch 24: Capacitors & Dielectrics
Ch 25: Resistors & DC Circuits
Ch 26: Magnetic Fields and Forces
Ch 27: Sources of Magnetic Field
Ch 28: Induction and Inductance
Ch 29: Alternating Current
Ch 30: Electromagnetic Waves
Ch 31: Geometric Optics
Ch 32: Wave Optics
Ch 34: Special Relativity
Ch 35: Particle-Wave Duality
Ch 36: Atomic Structure
Ch 37: Nuclear Physics
Ch 38: Quantum Mechanics

Intro to Forces + Newton's Laws

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Concept #1: Intro to Forces & Newton's Laws

Additional Problems
A rock attached to a string is whirled in a horizontal circle. If the string breaks suddenly, the rock will A) initially move radially outward from the center of the circle. B) initially move in a direction tangent to the circle. C) continue moving around the circle. D) drop straight down.
Under the influence of a constant force F, an object with mass m has acceleration a. Halving the force but doubling the mass will change the acceleration of the object to A) 4a B) the same a C) 1/2 a D) 1/4 a
Suppose someone is standing on a scale.  (a) Draw a free body diagram of the forces acting on the person (b) List what the scale would read if the person had a mass of 50 kg. Assume the units of the scale are N. (c) Do the normal force from the scale and the weight of the person form an action/reaction pair, as defined by Newton's third law?
If you were to move into outer space far from any stars on planets, A) both your weight and mass would change. B) your mass would change, but your weight would not change. C) your weight would change, but your mass would not change. D) neither your weight nor your mass would change. E) None of these is true.
A 165 lb researcher received a shipment of lab equipment in a 1600 N crate. She pushes it across the floor applying a 115 N force with her hands. Which of the following is true? A) She always feels a 115 N force from the crate pushing back against her hands. B) The crate will push back at her with a force of 165 lb. C) She will feel a 1600 N force from the crate pushing back at her. D) Only if the crate does not move will she feel a force of 115 N. E) She will feel it pushing back at her with less than 115 N, if the crate is moving forward.
In outer space, where there is no gravity or air, an astronaut pushes with a force of 25 N on a 2 kg moon rock with one hand and force of 25 N on a 4 kg moon rock with the other. Which of the following is true? A) Both rocks will push back at the astronaut with 25 N. B) Since the astronaut is weightless, he cannot push on the rocks. C) Since both rocks are weightless, they do not push back on the astronaut. D) The 4 kg rock pushes back on the astronaut twice as hard as the 2 kg rock. E) Since both rocks are weightless, they will have the same acceleration. 
A child weighs 335 N. What is the child's mass?A) 3286.4 kgB) 75.3 kgC) 335.0 kgD) 1488.9 kgE) 34.1 kg
A book is at rest on an incline as shown above. A constant force vertically downward is in contact with the book. The following figures show several attempts at drawing free-body diagrams for the book. Which figure has the correct directions for each force? The magnitudes of the forces are not necessarily drawn to scale.
Despite a very strong wind, a tennis player manages to hit a tennis ball with her racquet so that the ball passes over the net and lands in her opponent’s court. Consider the following forces:1. A downward force of gravity.2. A force by the “hit”.3. A force exerted by the air.4. A force exerted by the ground.Which of the above force(s) is (are) acting on the tennis ball after it has left contact with the racquet and before it touches the ground?1. 2 and 4.2. 2 only.3. 1 only.4. 1 and 2.5. 1, 2, and 3.6. 2 and 3.7. 1, 2, 3, and 4.8. 3 only.9. 1 and 3.10. 1, 3, and 4.
A 140-lb restaurant manager received a shipment of frozen meat in a 1600 N crate. She pushes it across the floor applying a 90 N force with her hands.A) She will feel it pushing back at her with less than 90 N, if the crate is moving forward.B) She will feel a 1600 N force from the crate pushing back at her.C) The crate will push back at her with a force of 140 lb.D) She always feels a 90 N force from the crate pushing back against her hands.E) Only if the crate does not move will she feel a force of 90 N.
In outer space, where there is no gravity or air, an astronaut pushes with an equal force of 15 N on a 3-kg moon rock and on a 6-kg moon rock.A) Since both rocks are weightless, they will have the same acceleration.B) Since both rocks are weightless, they do not push back on the astronaut.C) The 6 kg rock pushes back on the astronaut twice as hard as the 3-kg rock.D) Both rocks will push back at the astronaut with 15 N.E) Since the astronaut is weightless, he cannot push on the rocks.
An object is moving to the right, and experiencing a net force that is directed to the right. The magnitude of the force is decreasing with time. The speed of the object isA) constant in time.B) increasingC) decreasing
A box, mass 3.5 kg, sits on a horizontal frictionless table. A 11 N force is applied to the box at an angle 27° below the horizontal. What is the resulting acceleration of the box?A) 3.2 m/s2B) 2.8 m/s2C) 2.4 m/s2D) 3.5 m/s2E) 1.1 m/s2
Which of the following statements about forces is  not correct?A) In order for an object to turn, a force must be applied on itB) In order for an object to change speed, a force must be applied on itC) An object can put a force on another object without feeling a force in response; it depends on the objectsD) If an object feels a weight mg due to the Earth, then the Earth must feel a force mg in the opposite direction
A body moves in a straight line with a constant speed. Which of the following must be true?A) There is no net force acting on the body.B) There is a centripetal force acting.C) There is a constant net force acting in direction of motion. D) There is a single constant force acting in direction of motion.
Newton's Third Law of Motion says: Forces always come in pairs: when one object exerts a force on a second object, the second exerts an equal and opposite force on the first. If you pull horizontally on a door handle (action) this second force (reaction) isA) the frictional force of the floor against the soles of your shoes.B) the force that the door handle exerts on your hand.C) directed vertically down.D) the dark force.E) the force that the door exerts on the hinges.