work and energy examples CGS by h378WqK


									work and energy examples CGS

Short Answer

      1. How much work must you do to lift a 16 kg bucket full of water from the bottom of a well 13.8
         meters deep?

      2. What is the velocity of a 15.000 kg projectile with a kinetic energy of 1.6  10       Joules?


           A Hotwheel ™ car reaches the bottom of the track with a velocity of 2.1 m/s. What is the
           highest from the floor it can possibly get up the section of track it is approaching?


      4. Silly Suzzy swings on a swing set. She sees a spectacular scene from the peak of her swing.
         She has an altitude of 2.0 meters when she changes direction. How fast will she be moving
         when her altitude is 0.5 meter?

           How much kinetic energy does a 11 milligram bug have when her velocity is 67 cm/sec?


           A box pulled at a constant velocity of 3.0 m/s by a rope inclined 24.0 deg. The mass of the
           box is 53.0 kg. There is kinetic friction coefficient of 0.26 between the box and the floor.

           a. What is the tension in the rope?

           b. How much work is done moving the box 10.0 meters?

           c. What power is required to pull the box at this velocity?



      7. A spring is compressed 13.0 cm. Its spring constant is 110.0 N/m.

           a) How much force is required to compress it?
     b) How much energy is stored in it?

     c) The spring is used to launch a 30 gram ball vertically. How high above the springs
     equilibrium position will the ball rise?


8. An 440 kg sailplane (no engine) is at an altitude of 2,000 meters and has a velocity of 7 m/s.
   The pilot pushes forward on the stick and the plane noses down into a dive.

      (a) Ignore drag (wind resistance). How fast will the sailplane be going at an altitude of
     1,100 meters?

     (b) If his velocity is 85.1 m/s at 1,100 meters altitude, what was the work of friction done by
     the air on the airplane?

     A 1100 kg car accelerates up a 3 deg hill. Its velocity is 16 m/s and acceleration is 3 m/s 2.
     The drag on the car is 165 N.

     Draw a freebody diagram, label all forces.
a) What is the force that the wheels exert on the road?

b) What power is the motor producing under these conditions?

c) The chemical bonds of the car’s fuel store 1,400 J/g. How many grams of fuel are
burned very second if the motor is 100 percent efficient at converting the chemical energy of
the fuel into kinetic and potential energy of the car?

d) How fast must the fuel burn if the motor is only 79 percent efficient?
work and energy examples CGS
Answer Section


     1. ANS:
        W=16(9.8)13.8 = 2200 Joules

        PTS: 1
     2. ANS:

        PTS: 1
     3. ANS:


             v 2 2.12
        h            .23m
             2 g 19.6

        PTS: 1
     4. ANS:


        vbot=sqrt(19.6(2.0-0.5))=5.4 m/s

        PTS: 1
     5. ANS:
        mass = m(mg)/1,000,000
        v(m/s)= v(cm/sec)/100

        KE=1/2mv2 = 2.5  10        Joules

        PTS: 1
     6. ANS:
        a. Tcos (24.0) -mukmg=0
      T=mukmg/cos(24.0)=148 N

      b. W=Fdcos(24.0)=148(10.0)cos(24.0)=1350 J

      c. P=Fvcos(24.0) = 148(3.0)cos(24.0) = 405 watts

      PTS: 1


    7. ANS:

       PTS: 1
    8. ANS:

       PTS: 1
    9. ANS:
PTS: 1

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