A pile-driver weighing 200 lb. falls through 5 feet and drives a pile which weighs 600 lb. through a distance of 3 inches. Find the average resistance offered to the motion of the pile, assuming that the two remain in contact after the blow. How many foot pounds of energy are dissipated during the blow?
A smooth sphere impinging on another one at rest; after the collision their directions of motion are at right angles. Show that if they are assumed perfectly elastic, their masses must be equal.
A particle is suspended from a fixed point by a light elastic string. Show that the period of vertical oscillation is that of a simple pendulum of length \(l-l_0\), where \(l\) is the equilibrium length of the string and \(l_0\) its natural length. If the oscillations are of amplitude \(a\) and if when the particle is at the lowest point of its path it receives a downward blow which gives it a velocity \(u\), show that the time from the lowest to the highest point of the new path is \[ \sqrt{\frac{l-l_0}{g}} + \sqrt{\frac{l-l_0}{g}}\left\{\pi-\tan^{-1}\left(u\sqrt{\frac{l-l_0}{a^2g}}\right)\right\}. \]
Any point \(X\) is taken in the side \(CD\) of a rectangle \(ABCD\), and the line through \(A\) perpendicular to \(AX\) cuts \(BC\) in \(Y\). Prove that, if \(XY\) cuts \(BD\) in \(N\), then \(AN\) is perpendicular to \(XY\).
\(AOA'\) is a fixed diameter of an ellipse whose centre is \(O\), and \(P,Q\) are points in which the ellipse is cut by a pair of conjugate diameters. Prove by orthogonal projection or otherwise that the locus of the point of intersection of \(AP\) with \(A'Q\) is a similar ellipse whose centre lies on the given ellipse.
Prove that \(a+b+c+d\) is a factor of the expression \[ 2(a^4+b^4+c^4+d^4)-(a^2+b^2+c^2+d^2)^2+8abcd. \] Shew that \(a+b-c-d\) is also a factor, and find the remaining factors.
Shew that, if \(b\) is small compared with \(a\), the expression \((a-b)^n/(a+b)^n\) is approximately equal to \((a-nb)/(a+nb)\). When \(n<\frac{1}{2}\), and \(b/a < 10^{-2}\), determine the degree of approximation.
Prove that \[ \cos 7x - 8\cos^7x = 7\cos x\cos 2x\left(\cos 2x - 2\cos\frac{\pi}{5}\right)\left(\cos 2x - 2\cos\frac{3\pi}{5}\right). \]
The sides of a parallelogram are \(a\) and \(b\) and the acute angle between them is \(\alpha\); the acute angle between the diagonals is \(\theta\). Prove that \[ (a^2-b^2)\tan\theta = 2ab\sin\alpha. \] Determine the greatest value of the acute angle of a parallelogram whose diagonals have given lengths \(p\) and \(q\).
A variable line passes through a fixed point \((a,b)\) and cuts the co-ordinate axes in \(H\) and \(K\). The lines drawn through \(H\) parallel and perpendicular to a given line \(y=mx\) cut the axis \(x=0\) in \(Y\) and \(Y'\); and the lines drawn through \(K\) parallel to \(HY\) and \(HY'\) cut the axis \(y=0\) in \(X\) and \(X'\). Shew that the lines \(XY'\) and \(X'Y\) each pass through a fixed point which lies on a line that passes through the origin and is independent of \(m\).