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
(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
(i) Mechanical advantage = Load
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
