Physics Paper 2, Nov/Dec. 2011  
Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
General Comments

Question 12

 (a)  (i)   What is mechanical energy?

      (ii)    A ball of mass M raised to a height H above the ground is allowed to fall freely towards
              the ground.  Show that at a point T when it has fallen through a distance h, the total
              mechanical energy remains unchanged.

(b)    (i)   What is a thermometric property?
        (ii)    Copy and complete the table below

Thermometric substance

Thermometric property

Kind of thermometer













(c)       An inclined plane is used to raise a box 25.0 kg to the top of the plane by an
           effort of 180 N. Assume the plane is 60% efficient, calculate the:

           (i)    mechanical advantage;
          (ii)    velocity ratio;
         (iii)    angle the plane makes with the horizontal.
                                               [g = 10ms-2]


Part(a) this question on heat and mechanical energy was popular among the candidates  as majority of them were able to state that mechanical energy is the sum of the potential energy and the kinetic energy of a body.  The numerical question that followed was poorly attempted as many of them failed to show that mechanical energy of a falling body remains unchanged.

          Part(b) explanation of thermometric property was poorly rendered.  The completion of the table that followered was fairly attempted

           Part(c)  the problem on inclined plane was satisfactorily handled by most candidates that attempted it


           The expected answers are:

 (a)(i)    Mechanical energy is the ability of a body to do work by virtue of its
              motion and position                                                                                     



               At the top, total energy is potential  =  MgH                                                    
                As the ball passes point T, total mechanical energy  =  P.E + K.E                
                 =  Mg (H-h) + ½ Mv2                                                                                            

      Assume the body passes T with velocity  v
      Hence                              v2 = 2gh                                          

       At T,  total mechanical energy
                  =  Mg(H – h)  + ½  M2gh
                   =   MgH                                                                                                                

        Since total energy at T is the same as the initial energy at the top, it
        shows the energy remains unchanged.                                                                   


     (b)(i)   A thermometric properly is any physical measureable property which
                 changes/responds quickly, uniformly and regular with temperature such
                 that it  can be used to measure temperature.                                      



Thermometric substance

Thermometric property

Kind of thermometer






Liquid –in-glass


Platinium wire



Platinium resistance



Constant - Volume

Two metallic wires

Electron-motive force  




                    Mass of box  =  25kg  =  25 x 10  =  250N

       (i)    Mechanical advantage  =   Load

                                                        =  250

                                                         =  1.39                                                                   

      (ii)     Efficiency     =     M.A     x   100%                                                                

                             60  =  1.39     x     100

                              V.R   =   139
                                             60        =    2.31                                                                                  

     (iii)      V.R   =                                                                                                                     

                  2.31   =  

                  Sinθ    =    

                       =     Sin-1 ()                                                                                                  

                            =   25.7o   

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