Marks
2. State the Principle of Moments. Describe how you would set up a system of
four non-parallel forces in equilibrium. How would you use this apparatus
to verify the principle of moments ? (12)
FIXED BEAM
=r
LOAD
MOVABLE
WEIGHT
The bar AB of the weighing machine
shown in the sketch is 2\ ft long and
weighs 20 lb; the point of suspension C is
2 in from end A, and the centre of gravity
of the machine is 1 ft from the same end.
If the movable weight is 10 lb, what is
the maximum load that can be weighed ?
What change would you have to make
to this machine if you wished to weigh
approximately 500 lb ? (8)
3. Define the coefficient of static friction between two surfaces, and describe how
you would determine it experimentally. (1®)
A crate and contents weighing 2 cwt can be pulled along a horizontal floor at
a steady speed by a horizontal force of 56 lb wt. Calculate the force required
to keep the crate moving when an extra 1 cwt is added to it. What work is done
in the latter case when the crate is pulled a distance of 30 ft ? (6)
If, to the crate weighing 3 cwt, a force of 1 cwt wt is applied upwards at an
angle of 30° to the horizontal, what is the normal reaction ? vv
4. (a) State Boyle’s Law and describe an experiment to verify it. v'
{b) On a morning when the temperature is 12°C a tyre contains air at a pressure
of 28 lb per sq in. When the temperature rises to 30°C the tyre expands
in volume by 1 per cent. What is the new pressure of the air in the tyre ? \y)
(c)
A C
B
In the sketch of a steam safety valve
mechanism shown opposite, AB is a
light steel rod pivoted at A. The light
valve D has a surface area of f sq in.
What load should be hung at B if me
maximum steam pressure is to be 24 lb
per sq in ?
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