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

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 Mercury Liquid-in-glass Platinum resistance Gas Pressure Thermocouple

(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:

(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

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

(ii)

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 Mercury Volume/length Liquid –in-glass Platinium wire (Electrical) resistance Platinium resistance Gas Pressure Constant - Volume Two metallic wires Electron-motive force Thermocouple.

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

Effort

=  250
180

=  1.39

(ii)     Efficiency     =     M.A     x   100%
V.R

60  =  1.39     x     100
V.R

V.R   =   139
60        =    2.31

(iii)      V.R   =

2.31   =

Sinθ    =

=     Sin-1 ()

=   25.7o