P. 4138. A disc of radius 25 cm and of uniform density can swing (with a small amplitude) about a horizontal axle which is perpendicular to the plane of the base of the disc.
a) What is its period in seconds if the axle is 25 cm from the centre of the disc?
b) Where must the axle be placed in order that the period is to be 1 s?
c) Where must the axle be placed in order that the period is to be the minimum?
P. 4142. An object is at a distance of d from a screen. The convex lens, placed between them, forms the sharp image of the object at the screen at two different positions, the distance between these positions is s.
a) Find the focal length, f, of the lens.
b) Suppose that d is known very precisely. When will the uncertainty in the measurement of s cause a greater error in the calculation of f if the value of s is greater or if it is smaller?