
Questions and Answers for Topic #05
Topic #05 Concepts and Skills
Link to "Concepts and Skills"

Topic 5 Vocabulary:
Free Body Diagram: A diagram that shows the direction of the force operating on (acting on) each object. Force: A push or pull exerted on an object having magnitude and direction; it may be either a contact or long range force. Applied Force: A natural or man made force that is applied to an object. Net Force: The vector sum of all of the forces acting on an object. Force of Friction: The contact force that act to oppose sliding motion between two surfaces. Force of Gravity: The long range force due to gravitational attraction between two objects. For example, the earth and another object such as you exert a gravitational pull on one another. Weight: A measure of the force of gravity between two objects. (The unit of weight in the metric system is the Newton, N. The unit of weight in the British [English] system is the pound, lb.) Weight can also be defined by using the definition of the force of gravity. Displacement: The vector quantity that defines the distance and direction between two positions. Position: The location of an object on a coordinate system such as on a map of the earth where position is recorded in terms of latitude and longitude measurement, much in the same way as a point is expressed on a graph using x and y data values. Position Vector: The arrow on a motion diagram that is drawn from the origin to the moving object. Velocity: The vector quantity that defines the speed and direction of a moving object. Descriptive adjectives such as instantaneous, constant and average may be used along with this term. Acceleration: The vector quantity that defines the rate at which the speed of an object changes as well as the direction in which the change occurs. Descriptive adjectives such as instantaneous, constant and average may be used along with this term. Air Resistance: The opposition of the atmosphere to the forward movement of an object; it also called aerodynamic drag (force), which is the resistance of air to the movement of an object. It could also be described as air friction, the friction caused by air when an object passes through it. Terminal Velocity: The constant velocity of an object, that is achieved when the (aerodynamic) drag force equals the force of gravity and the falling object no longer accelerates because the net force acting on it is zero newtons. Variable Symbols: The symbols used in equations to represent the measurements
used in the solving of problems.

Review Questions:
Questions:
Section 6.2
Section 6.3

Application Questions:
Chapter 6
Questions 10. If you are in a car that is struck from behind, you can receive
a serious neck injury called whiplash.

Word Problems:
Problem Set #5: Follow the written directions unless indicated otherwise by your instructor. FORCE, MASS, and ACCELERATION: F = m a 1. An unbalanced force of 25N, E, is applied to a 12 kg mass. What is the acceleration given to the mass? 2. An unbalanced 16N force is applied to a 2 kg mass. What is the acceleration of the mass? 3. A shotputter exerts an unbalanced force of 140N on a shot giving it an acceleration of 19 m/s^2. What is the mass of the shot? 4. A 1.5 kg mass accelerates across a smooth table at 16 m/s^2. What is the unbalanced force applied to it? 5. An object moving with a constant velocity has an unbalanced
force applied to it. If the
6. An unbalanced force of 965N causes an object to accelerate at 54.5 m/s^2. What is the mass of the object? 7. Determine the acceleration that an unbalanced force of 25 N gives to a 4.0 kg mass. 8. A racing car undergoes a uniform acceleration of 8.00 m/s^2. If the unbalanced force causing the acceleration is 6.00 x 10^3 N, what is the mass of the racing car? 9. A racing car has a mass of 710 kg. It starts from rest and travels 120 m in 3.0 s. The car undergoes uniform acceleration during the entire 3.0 s. What unbalanced force is applied to it? 10. An artillery shell has a mass of 55 kg the shell is fired from the muzzle of a gun with a speed of 770 m/s. The gun barrel is 1.5 m long. What is the average force on the shell while it is in the gun barrel? MASS and WEIGHT: W = m g 11. Determine the weights of these masses.
12. Determine the mass of these weights.
13. How much force is needed to keep a 20 N stone from falling? 14. An economy car has a mass of 800 kg. What is its weight? 15. A car has a mass of 1000 kg. What is its weight? 16. A small yacht weighs 14,700 N. What is its mass? 17. A 7.5 kg object is placed on a spring scale. If the spring scale reads 78.4 N, what is the acceleration of gravity at that location? 18. A car has a mass of 1200 kg. How much would the car weigh on the moon? (the moon's gravitational acceleration is 1.6 m/s^2. NORMAL FORCE, FRICTION, and COEFFICIENT OF FRICTION: F(f) = m F(N) 19. A horizontal force of 18N is necessary to pull a 52 N sled across a cement sidewalk at a constant speed. What is the coefficient of sliding friction between the sidewalk and the metal runners of the sled? 20. The sled in problem 19 is then placed on packed snow. If a 650N boy sits on the sled, what will be the force necessary to slide the sled at a constant speed? The coefficient of sliding friction is 0.012 for the sled runners on packed snow. NET FORCE and ACCELERATION: F(net) = F(a) + F(f) or F(net) = F(a)  F(f), Fnet is the force that produces acceleration. (F = ma); note that the use of the addition form of the equation forces you the reader into taking responsibility for inserting negative values for scenarios where there are opposing forces, whereas using the subtraction form of the equation allows you to solve the problem using only the magnitudes of the measurements. 21. A rubber ball weighs 49 N. What is the acceleration of the ball if an upward force of 69N is applied? 22. a. What is the weight of a 20.0 kg stone?
23. A rocket weighs 9800 N.
24. An object with a mass of 22.7 kg is placed on a surface. the mass moves horizontally at a constant speed. The coefficient of sliding friction between the two surfaces is 0.94. What is the force of friction? 25. A car moving on a level highway has a mass of 4.0 x 10^2 kg. The coefficient of friction between the tires and the highway is 0.19. What acceleration will a force of 2250 N produce on the car? 26. A small rocket weighs 14.7 N.
27. A force of 91 N is exerted straight up on a stone that has
a mass of 0.75 kg. Calculate
28. A rocket that weighs 7840 N on the earth is fired. The
force of propulsion is +10440 N. Determine:
29. The instruments attached to a weather balloon have a mass
of 5.0 kg.
