A particle of mass $$m$$ is moving in a horizontal circle of radius $$r$$ under a centripetal force given by $$\left(-k / r^2\right)$$, where $$k$$ is a constant. Then
A plane glass mirror of thickness $$3 \mathrm{~cm}$$ of material of $$\mu=\frac{3}{2}$$ is silvered on the back surface. When a point object is placed $$9 \mathrm{~cm}$$ from the front surface of the mirror, then the position of the brightest image from the front surface is
A skylab or mass $$m \mathrm{~kg}$$ is first launched from the surface of the earth in a circular orbit of radius $$2 R$$ (from the centre of the earth) and then it is shifted from this circular orbit to another circular orbit of radius $$3 R$$. The minimum energy required to place the lab in the first orbit and to shift the lab from first orbit to the second orbit are
A train has to negotiate a curve of radius $$400 \mathrm{~m}$$. By how much should the outer rail be raised with respect to the inner rail for a speed of $$48 \mathrm{~km} / \mathrm{h}$$ ? The distance between the rails is $$1 \mathrm{~m}$$.