Monday 14 June 1965 9.30-12.30




Careless and untidy work will be penalized.





Answer seven questions.






1.   Two equal uniform rods AB. AC each of weight W and length 2a, and a third uniform rod of weight W1, are freely hinged together to form a triangle ABC in which the angle BAC is  . The triangle hangs in a vertical plane from a smooth pivot at B, and a couple is applied to the rod AB so as to keep the triangle in equilibrium with BC horizontal and A below BC. Find (i) the moment of the couple, showing its sense in a diagram, and (ii) the horizontal and vertical components of the forces exerted on AC by BC and AB.



84 ADV. EE                                                                           Turn over

2.   A uniform rod AB of weight W and length 4a rests on a fixed cylinder of radius whose axis is horizontal. The rod is also horizontal, perpendicular to the axis of the cylinder, and the point of contact is C where AC is of length a. It is kept in this position by a light smooth string, attached to A, which rests against the surface of the cylinder and has a weight W1 hanging at its other end. Prove the geometrical fact that at A the angle between the rod and the string is 1200, and hence find the ratio of the weights W1 and W.

Find the normal reaction and the frictional force at C, and prove that the coefficent of friction at this point must be greater than or equal to


3.   A uniform wire is bent to form a circular arc subtending an angle  at the centre. Prove that the distance  of the centre of mass from the centre of the circle is  where r is the radius.

A uniform wire in the form of a semicircle of radius r rests against a smooth vertical waIl and is in a vertical plane perpendicular to the wall with its middle point in contact with the wall   It is kept in equilibrium in this position by means of a light string of appropriate length joining a point B which divides the length of the wire in the ratio 1 : 3 to a point A on the wall. Explain how to fix the direction of the string and prove that it makes an angle  with the horizontal where



If the weight of the wire is W, find the reaction at the point of contact with the wall.


4.   A light inextensible string of length l is threaded through a smooth bead of mass m and has one end fixed at a point A on a smooth horizontal table and the other at a point B at a height  vertically above A. The bead is projected so as to describe a circle in contact with the table with angular velocity . Find the radius of the circle. Prove that the tension in the string is , and that  must not exceed a certain value. Find this value.


5. A light elastic string, of natural length a and modulus 2mg, is attached at one end to a fixed point A on a smooth horizontal table and at the other end to a particle P of mass 2m. A second light string which is inextensible is attached to P and has at its other end a second particle Q of mass m. The distance from A to the edge of the table is 2a. Initially the string PQ passes over the edge, the plane APQ’ is perpendicular to the edge, and Q hangs below the edge. P is held on the table with the elastic string just taut and then released. Write down the equations of motion for P and Q when the distance AP is .   Hence find the differential equation of the motion, and the time taken for P to reach the edge of the table.


Find also the tension in each string just as P reaches the edge of the table.


6. An engine of mass 56 tons moves from rest on a horizontal track against constant resistances, and for the first 30 seconds of its motion its acceleration is ft. per sec2  where t seconds is the time from the start. If the force exerted by the engine is initially   tons wt., find the magnitude of the resistances and an expression for the force exerted by the engine while t is less than 30, giving both answers in tons wt.


Calculate the speed of the engine after 21 seconds and the horsepower at which it is then working.


(Take g as 32 ft. per sec.)


7. An aircraft flying straight and level at constant

speed passed over two landmarks A and B, where B is

540 miles N.E. from A. If the wind was blowing at

60 m.p.h. from due north and the speed of the aircraft

in still air is 300 m.p.h. find the course on which it was

flying and the time taken for the distance AB.

On the return journey the time taken for the same distance was 1 hr. 40 mins. If the speed of the wind was the same but its direction was from  W. of N.,  being acute, find the value of


84 ADV



8.   A ring of mass m can slide on a smooth vertical rod and is attached to a light inextensible string which passes over a smooth peg at a distance a from the rod. At the other end of the string hangs a particle of mass M.   The ring is released from rest at a point level with the peg and drops a distance x while the particle rises a distance y. Express y in terms of x,  find  in terms of x and dx/dt and write the equation of energy for the system.


Given that . prove that when


and that the system first comes to rest when



9.   Two equal particles are  projected at the same instant from points A and B at the same level,  the first from A towards B with velocity u at 450 above AB. and the second from B towards A with velocity v at 600 above BA.   If the particles collide directly when each reaches its greatest height, find the ratio  and prove that , where a is the distance AB


After the collision the first particle falls vertically. Show that the coefficient of restitution between the particles is .