PHY11L - E202 CONSERVATION OF MOMENTUM: THE BALLISTIC PENDULUM

EXPERIMENT 202 :  CONSERVATION OF MOMENTUM: THE BALLISTIC PENDULUM

 

 















 


DATA and OBSERVATIONS

 

 

TABLE 1. Getting  the Initial Velocity of the Steel Ball, Ballistic Method

 

 

 

mass of the steel ball,  =    65.875   ­­­­­­ g           mass of the pendulum, =    241.40  ­­­­­­ g          

 

 

TRIAL

Angle

 

1

 

 25         o

 

Initial height of the pendulum  

            

 

        =          3.0000      cm

 

2

 

25         o

 

Final height of the pendulum

                 

 

        =         6.4500       cm

 

3

 

25         o

 

Increase in height, 

             

 

 

 

         =          3.4500       cm

4

 

25         o

 

Velocity of the steel ball and the pendulum right after collision,

                

 

 

 

         =         82.231          cm/s

5

 

25         o

 

Velocity of the pendulum before collision

        

 

        =           0                cm/s

 

 

 

Average angle:             25         o

 

Velocity of the steel ball before collision,

                     

     

 

      

 

     

         =      387.57           cm/s

 












































 

TABLE 2. Getting  the Initial Velocity of the Steel Ball,  Trajectory Method

 

Gravitational constant, g = 980 cm/s2

 

TRIAL

Horizontal

Distance,

 

 

Height from the reference point to the ground

 

          =       82.000     cm

1

 153.10   cm

2

154.20   cm

3

152.60   cm

 

Velocity of the steel ball before collision,

           

 

        

 

        

          =      357.33        cm/s

4

153.50   cm

5

154.30   cm

 

Average :        153.54   cm

 

 





















TABLE 3.  Determining the Percentage Difference

 

Percentage Difference ,

                      % diff=

 

 

 

Percent difference =          2.17         %

 

 

                                   













 

  GUIDE QUESTIONS

 

1.   Suppose a ball with half the mass is used and is projected out of the launcher with the same speed. How   

     does the increase in height of the system now compared with that when the original ball was used? Defend  

     your answer.

 

 If we used a ball with half mass with the same initial speed, the resulting increase in height will be smaller than the original mass but not exactly half the original increase in height. The height when half of the mass is used is less than the increase in height when the original ball was used.

 

  Considering the results given on the data sheet:

 

  m1 = 65.875/2 = 32.9375 g  

  m2 = 238.7 g                                                          

   v1 = 498.88 cm/s                                                   yn = 1.867 cm < 5.4 cm

           

   v1 =   (   2gy)(m1 + m2)/ m1

 

   

2.    Suppose the launcher is positioned higher above the table top. How does this change affect the computed 

      initial speed of the ball? Defend your answer.

 

              When the launcher is positioned higher above the table top, the initial speed of

            the ball will still be the same because as we can recall the lessons in kinematics,

            the horizontal velocity of the projectile is always constant, Thus, whenever the

            height increases, the range also increases proportionally making the initial                 

            velocity of the ball the same which can be computed using the formula:

 

 

 

3.    A 50 gram bullet is fired horizontally into a 5 kg block of wood suspended by a long cord. The bullet sticks in

      the block. Determine the velocity of the bullet if the inelastic collision causes the block to swing 0.10 m    

      above its initial.

    m1 = 0.005 kg                                          

    m2 = 5 kg

    y = 0.10 m

                                   

  V1 = (0.005 + 5 kg)    2(9.8) (0.1m)

            0.005 kg

 

 V1 = 1,401.4 m/s

   

 

 

 

 

ANALYSIS

   1.  Which method (ballistic method or trajectory method) is more accurate in determining the initial speed of    

        the ball. Defend your answer.

              

     The ballistic method is more accurate in finding the initial speed of the ball

    because unlike the trajectory method, we do not need to find the horizontal

    displacement of the ball. The horizontal displacement of the ball (x) is also

    not accurate since there could always be a small margin of error if you

    measure it with the use of a meter stick. Using the ballistic method, we only

    need to determine the increase in the height of the pendulum, and compute

    the intial velocity using the equation:

 

 

   Using this formula of the ballistic method, we can have a more accurate result    

    than using the trajectory method.

 

 2.  In Part 1 of the experiment, is the total momentum of the system conserved? Explain.

 

        Yes, the total momentum of the system is conserved. In part 1 (Ballistic

         method), the ballistic method is an example of an inelastic collision. The

         law of conservation states that in an inelastic collision, the total momentum

          of the system is always conserved.

 

   3.  In Part 1 of the experiment, when is the total energy of the system not conserved? When is the total

        energy of the system conserved?     

      

        The total energy of the system is conserved during the collision. The total

       momentum before an inelastic collision is the same as after the collision.

       Since what is asked is the total energy not the total kinetic energy, the total

       energy is conserved because the total kinetic energy before and after the

       inelastic collision is different. Of course this does not mean that total energy

       has not been conserved, rather the energy has been transformed into another

       type of energy.

       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CONCLUSION

     1.  What causes the total momentum of the system to change?                                                     

 

 

        Momentum, like mass, is also a conserved quantity, and there is a law that

        states that "the momentum in an isolated system is constant". This law is the

        law of conservation of momentum. The law of conservation of momentum is

        very useful in the analysis of collisions and explosions as it can be used to

        calculate the velocities of a body or bodies before and after the collision.

        Since momentum is a conserved quantity, external forces such as air resis-

        tance are the one that causes the total momentum of a system to change.

 

 

 

     2.  When the total momentum of the system is conserved, is the total energy of the system conserved

          as well? Explain.

 

 

         Yes, both the energy and the momentum of the system are conserved. In an     

          elastic collision, both kinetic energy and momentum is conserved. In an

          inelastic collision, the total momentum is also conserved but the total

          kinetic energy is not. An inelastic collision is usually accompanied by defor-

          mation of one or both bodies. This requires energy thus; the total energy

          is conserved but not necessarily the kinetic energy.

 

 

 

     3.  Is the total momentum of the system conserved in all kinds of collisions? Explain.

          

 

          Yes, the total momentum in all kinds of collisions is conserved. In an elastic

         collision, both energy and momentum is conserved. In an inelastic collision,

         the total momentum is conserved but total kinetic energy is not conserved

         the kinetic energy is transformed into other kinds of energy. Also, the law of

         conservation of momentum states that the total momentum of the system

         before collision is equal to the total momentum of the system after collision.

        

         

 

 

 

3 comments:

  1. Anonymous08:28

    hoy brad, alam ko late na to pero mali sagot mo sa velocity

    dapat .05kg hindi .005 haha :p

    ReplyDelete
    Replies
    1. Anonymous22:55

      hoy ka din. di na pwede balikan ang nakalipas, okay?

      Delete
    2. Anonymous23:02

      bitter ka. move on din pag may time!!!

      Delete

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