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 $$1 \mathrm{~m}$$.
From Wien's displacement law, $$\lambda_m T=$$ constant $$=0.00289 \mathrm{~m}-\mathrm{K}$$
Radiation from moon givens $$\lambda_m=4700 \mathop A\limits^o$$ and another wavelength of $$14 \times 10^{-6} \mathrm{~m}$$. Out of the following which conclusion(s) drawn is/are correct with the given information regarding the moon and the sun?
1. Sun radiations are reflected from moon's disc.
2. The temperature of moon's surface is $$207 \mathrm{~K}$$
3. The temperature of the sun is $$6160 \mathrm{~K}$$.
A disc of $$10.0 \mathrm{~cm}$$ diameter is rotated at speed of $$3600 \mathrm{~rpm}$$ inside a long solenoid of 1200 turns per metre on the axis of the solenoid and perpendicular to the plane of the disc. When a current of $$1.5 \mathrm{~A}$$ is passed through the solenoid, the difference in the potential between axes and circumference of the disc is nearly