# Newton's Laws Review

Unit 2

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### Part D: Drawing and Interpretting Free-Body Diagrams

26. Construct free-body diagrams for the following physical situations at the instant in time for which they are described. As is always done in free-body diagrams, label the forces according to type and draw the arrows such that their length reflects the magnitude of the force.

 a. A book is at rest on top of a table. b. A book is being pushed to the right across a table surface with a constant velocity. (Neglect Fair.) c. A book is being pushed to the right across a table surface and accelerating in the direction of the push. (Neglect Fair.) d. A student is pushing lightly upon a large box in an attempt to push it to the right across the floor, but the box fails to move. e. A rightward-moving box (which was previously set into rightward motion across the floor) gradually slows to a stop. f. An air track glider is gliding to the right at constant velocity. (Neglect Fair.) g. A ball is dropped from rest from the top of a building. (Neglect Fair.) h. Several seconds after being thrown, a football is moving upwards and rightwards towards the peak of its trajectory. (Neglect Fair.) i. Several seconds after being thrown, a football reaches the precise peak of its trajectory. (Neglect Fair.) j. A falling skydiver is speeding up. k. A falling skydiver has reached a terminal velocity. l. After reaching a terminal velocity, a falling skydiver has opened her parachute. m. A car is moving to the right at a high speed across a level roadway surface; the driver's foot remains on the gas pedal. n. A car is skidding to a stop (with wheels locked) while traveling to the right across a level roadway surface. o. An elevator (held by a cable) is moving upwards at a constant velocity. (Neglect Fair.) p. An upward moving elevator (held by a cable) slows down. (Neglect Fair.) q. A downward moving elevator (held by a cable) slows down. (Neglect Fair.) r. A picture hangs summetrically by two wires oriented at angles to the vertical.

Types of Forces || Drawing Free-Body Diagrams

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### Part E: Force-Mass-Acceleration Relationships

Construct free-body diagrams for the following objects; label the forces according to type. Use the approximation that g=10 m/s2 to determine the magnitude of all forces and the net force and acceleration of the object.

 27. A 2-kg box is at rest on a table.   ("At rest" would indicate a balance of forces and an acceleration of 0 m/s/s.) 28. A 2-kg box is free-falling from the table to the ground. ("Free-falling" indicates that the only force that influences the motion is the force of gravity.) 29. A 2-kg box equipped with a parachute is falling at a terminal velocity after being dropped from a plane. (A "terminal velocity" indicates a constant velocity and a balance of forces.)
 30. A 2-kg box is sliding to the right across a table. The force of friction upon the box is 5 N.   (Friction is directed opposite the motion and causes a leftward acceleration; no rightward force is spoken of, only a rightward motion.) 31. An 8-N force is applied to a 2-kg box to move it to the right across the table at a constant velocity of 1.5 m/s.   (A "constant velocity" indicates an acceleration of 0 m/s/s and a balance of forces.) 32. An 8-N force is applied to a 2-kg box to accelerate it to the right across a table. The box encounters a force of friction of 5 N. (The horizontal forces can be summed as vectors; divide by the mass to obtain the acceleration value.) 33. A 500-kg freight elevator is descending down the shaft at a constant velocity of 0.50 m/s. (A "constant velocity" indicates an acceleration of 0 m/s/s and a balance of forces.) 34. A 500-kg freight elevator is moving upwards towards its destination. Near the end of the ascent, the upward moving elevator encounters a downward acceleration of 2.0 m/s/s.   (Begin by multiplying m•a to find the net force - 1000 N, down. The downward gravity force must be 1000 N more than the upward tension force.) 35. A 150-N rightward force is applied to a 20-kg box to accelerate it to the right across a rough surface at a rate of 2.0 m/s/s.   (Begin by mulitplying m•a to determine the net force - 40 N, right. The rightward applied force must be 40 N more than the leftward friction force.)

Free-Body Diagrams | Finding Acceleration || Finding Individual Forces

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