An astronaut floating freely in space decides to use his flashlight as a rocket. He shines a $10$ $W$ light beam in a fixed direction so that he acquires momentum in the opposite direction. If his mass is $80$ kg,how long must he shine the light to reach a velocity of $1$ $m/s$?

$A$ point source of light is placed at the centre of curvature of a hemispherical surface. The source emits a power of $24 \, W$. The radius of curvature of the hemisphere is $10 \, cm$ and the inner surface is completely reflecting. The force on the hemisphere due to the light falling on it is $.......... \times 10^{-8} \, N$.

$A$ totally reflecting small plane mirror placed horizontally faces a parallel beam of light as shown in the figure. The mass of the mirror is $20 \, g$. Assume that there is no absorption in the lens and that $30 \%$ of the light emitted by the source goes through the lens. Find the power of the source needed to support the weight of the mirror in $MW$ (take $g = 10 \, m/s^2$ and $c = 3 \times 10^8 \, m/s$):-

Light with an average flux of $20 \, W/cm^2$ falls on a non-reflecting surface at normal incidence having a surface area of $20 \, cm^2$. The energy received by the surface during a time span of $1 \, minute$ is $............ \, J$.

Electromagnetic radiation of intensity $0.6 \ W/m^2$ is falling on a black surface. The radiation pressure on the surface is

$A$ radiation of energy $E$ falls normally on a perfectly reflecting surface. The momentum transferred to the surface is ($c$ is velocity of light).