SPH Quiz Forces Total

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                                                   Quiz 2 – Forces
K: ___/9 A: ___/16 I: ___/20 C: ___/4 Total: ____/55
                                                                  Name: _____________________________

Part A
Answer the questions below on the scantron.
           True and False {K – 6}

____    1. The reason your head feels like it jerks backward when pulling away from a stop sign is best explained by
           Newton's First Law.
____    2. The force that propels you forward as you walk across the floor is the force that is exerted by the floor itself.
____    3. If two forces that are identical in strength but exactly opposite in direction act on the same object, that object
           must necessarily be motionless.
____    4. A child sits on a toboggan and slides down a hill with a particular acceleration. If another child joins the first
           one on the toboggan, they will slide down the hill with the same acceleration.
____    5. When drawing a proper free-body diagram, all forces, including the net force acting on the object, must be
           clearly indicated.
____    6. Two people pushing an object across a frictionless surface will result in twice the acceleration than if only one
           person pushes. Assume the object slides in both cases and that both people push with the same force.

            Multiple Choice {I – 18}

____    7. An elevator is suspended by a cable and moves upward. Which of the following free-body diagrams best
           represents the forces acting on the elevator?

           a. A                                          d. D
           b. B                                          e. E
           c. C
____    8. Which of the following free-body diagrams best represents the forces acting on an astronaut in orbit around
           the Earth?

            a. A                                              d. D
            b. B                                              e. E
            c. C
____    9. A stone is tied to the end of a string and twirled around in a circle which describes a vertical plane. Which of
           the following free-body diagrams best represents the forces acting on the stone at the top of the circle?

         a. A                                         d. D
         b. B                                         e. E
         c. C
____ 10. Study the free-body diagram below and choose the statement that best describes the object's motion.

         a. The object will accelerate north.
         b. The object will be motionless.
         c. The object will accelerate northeast.
         d. The object will travel with uniform motion.
         e. The object will travel north with a constant velocity.
____ 11. Study the free-body diagram below and determine what additional force(s) would be required for the object to
         achieve uniform motion.

            a. 1 N [W]                                       d. 2 N [S] and 1 N [E]
            b. 1 N [E]                                       e. 2 N [S] and 1 N [W]
            c. 2 N [N] and 1 N [W]
____ 12. The free-body diagram below represents a 200-g rock suspended by a string. What is the rock's acceleration?

           a. 6.2 m/s2 [up]                                   d. 6.2 x 10–3 m/s2 [up]
           b. 33 m/s [down]                                   e. the rock does not accelerate
           c. 0.25 m/s2 [down]
____ 13.   How much force would you have to apply to just support the weight of an average apple of mass 1.0  102 g?
           a. 9.8  103 N [up]                                d. 9.8  100 N [up]
           b. 9.8  10 N [up]
                                                              e. 9.8  10–1 N [up]
           c. 9.8  10 N [up]

____ 14.   Which of the following observations is explained by Newton's first law?
           a. kicking your feet against something solid to remove snow from your boots
           b. feeling as though you're being rocked from side-to-side on a roller coaster
           c. an apple hanging motionless from the limb of a tree
           d. feeling as though your head jerks backward when pulling away at green light
           e. all of the above
____ 15.   A heavy crate is pushed across a rough surface. The force that is ultimately responsible for the crate's motion
           is the
           a. applied force                                   d. net force
           b. frictional force                                e. normal force
           c. gravitational force
____ 16.   A 2.5  103 kg car is travelling due west at 30 m/s when the brakes are applied, exerting a force of 5.0  103 N
           [E]. What is the car's acceleration due to the braking?
           a. 2.0 m/s2 [W]                                    d. 15 m/s2 [E]
           b. 2.0 m/s [E]                                     e. 2.0 m/s [E]
           c. 15 m/s2 [W]
____ 17.   A hockey puck of mass 150 g is sliding south along the ice and slows at a rate of 1.2 m/s 2 . What is the net
           force acting on the puck?
           a. 1.8  102 N [N]                                 d. 1.8  10-1 N [N]
           b. 1.8  10 N [S]
                                                              e. 1.9  10-1 N [S]
           c. 1.8  10 N [N]

____ 18.   If the force of gravity that the earth exerts on you is considered to be the action force then, according to
           Newton's third law, the corresponding reaction force would be the
           a. normal force of the Earth acting upward on you
           b. force your feet exert downward on the Earth
           c. force of gravity you exert on the Earth
           d. force you exert on your feet, pressing them against the Earth
           e. force of gravity the Earth exerts on everything else
____ 19. How much would a 60-kg person weigh on the Moon where the gravitational field strength has a magnitude
         of 1.6 N/kg?
         a. 60 kg                                         d. 98 N
         b. 96 kg                                         e. 96 N
         c. 98 kg
____ 20. If you weighed 112 N on the Moon where g = 1.6 N/kg, how much would you weigh on Earth?
         a. 1.1  102 N                                   d. 1.1  104 N
         b. 1.7  104 N                                   e. 6.9  103 N
         c. 6.9  10 N 2

____ 21. The value of "g" at the surface of Mars is 3.7 N/kg. How much would a 60.0-kg person weigh at an altitude
         above the Martian surface equivalent to the planet's radius?
         a. 2.2  102 N                                   d. 56 N
         b. 1.6  10 N 2
                                                          e. 28 N
         c. 1.1  102 N
____ 22. Study the force system diagram pictured below and select the factor which would NOT influence the amount
         of kinetic friction.

         a. object's mass, m                              d. applied force, FA
         b. coefficient of kinetic friction, K           e. gravitational field strength, g
         c. normal force, FN
____ 23. Which of the following statements concerning friction is true?
         a. The frictional force always acts oppositely to the applied force.
         b. For two given surfaces, the coefficient of static friction is generally greater than the
            coefficient of kinetic friction.
         c. Friction is a force which is unavoidable and serves no practical purpose.
         d. Two very highly-polished surfaces in contact with one another will have very little friction
            between them.
         e. Friction always acts in the direction of motion.
____ 24. A chalk brush sits on a metre stick as pictured in the diagram. As one end of the metre stick is elevated, the
         chalk brush eventually begins to slide. Why?

            a.   The coefficient of friction changes.
            b.   The gravitational force on the brush changes.
            c.   The normal force on the brush changes.
            d.   The gravitational force begins to act along the metre stick.
            e.   An applied force is created.

Part B
For all calculation questions make sure to show all your work including formulas.

                 1. Give an example that clearly illustrates Newton's second law. {I – 2}

                 2.     All forces act "by" something and act "on" something. The system diagram below illustrates a crate
                      being pushed across a floor by a person. FA is the force exerted by the person on the crate. What do
                      the other forces represent? {K – 3}
3. A hockey puck of mass 3.50  102 g is sliding along the ice at 6.0 m/s [N] when it hits a rough patch
   that exerts a frictional force of 0.42 N [S].
       a. Draw the free-body diagram of the puck while it slides on the rough section. {C – 2}
       b. Determine the puck's acceleration. {A – 2}
       c. Determine how far the puck will slide before stopping once it hits the rough section. {A – 2}

4. A stationary box of mass 4.2 kg is given a push of 8.2 N [S] along a surface where the frictional force
   acting is 5.8 N [N]. The push lasts for 3.6 s and then the box is allowed to slide on its own until it
   comes to rest.
       a. Draw free-body diagrams to show the box being pushed and sliding on its own. {C – 2}
       b. Determine the acceleration of the box as it is being pushed. {A – 2}
       c. Calculate the speed of the box just as the push ceases. {A – 2}

5. Looking from above, three ropes are tied to a 8.0-kg object with forces being exerted as indicated.
   What is the object's acceleration? {A – 2}
6. An applied force of 6.2 N acts on a 2.1-kg object, pushing it horizontally across a surface where the
   coefficient of kinetic friction is 0.15.
       a. Determine the frictional force acting. {A – 2}
       b. Determine the object's acceleration. {A – 2}

7. How much force would be required to start a 1.0-kg object sliding along a horizontal surface if the
   coefficient of starting friction is 0.20? {A – 2}

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