The tidal waves in the sea are primarily due to

Find the acceleration of our galaxy due to the nearest comparably sized galaxy. The approximate mass of each galaxy is $8 \times 10^{11}$ solar masses,and they are separated by $2 \times 10^6$ light-years. Each galaxy has a diameter of $10^5$ light-years. (Assume $1 \text{ light-year} \approx 10^{16} \text{ m}$,gravitational constant $G \approx 10^{-10} \text{ Nm}^2/\text{kg}^2$,and mass of the Sun $= 2.0 \times 10^{30} \text{ kg}$)

$A$ uniform sphere of mass $M$ and radius $R$ is surrounded by a concentric spherical shell of the same mass but radius $2R$. $A$ point mass $m$ is kept at a distance $x$ $(R < x < 2R)$ in the region bounded by the spheres as shown in the figure. The net gravitational force on the particle is:

An astronaut of mass $m$ is working on a satellite orbiting the Earth at a distance $h$ from the Earth's surface. The radius of the Earth is $R$,while its mass is $M$. The gravitational pull $F_G$ on the astronaut is

Two metallic spheres each of mass $M$ are suspended by two strings each of length $L$. The distance between the upper ends of the strings is $L$. The angle which the strings will make with the vertical due to the mutual attraction of the spheres is

The gravitational constant depends upon .........