# 21 - Gravitation Questions Answers

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

If L is the angular momentum of a satellite revolving around earth is a circular orbit of radius r with speed v, then (i) L α v

(ii) L α r

(iii) L α √v

(iv) L α √r

Joshi sir comment

L = m*v*r

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

If potential energy of a body of mass m on the surface of earth is taken as zero then its potential energy at height h above the surface of earth is [ R is radius of earth and M is mass of earth]

Joshi sir comment

[-GMm/(R+h)]-[-GMm/R] = GMm[1/R - 1/(R+h)]

solve ?

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

Two points masses having m and 4m are placed at distance at r. The gravitational potential at a point, where gravitational field intensity zero is

Joshi sir comment

field intensity at distance x from m = Gm/x2 - G4m/(r-x)2

compare it to 0 and find x

then calculate gravitational potential at the point

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

During motion of a planet from perihelion to aphelion the work done by gravitational force of sun on it is positive or negative.

Joshi sir comment

change in K E = work done by all the forces

and from perihelion to aphelion velocity decreases

so work done will be negative

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

If an object is projected vertically upwards with speed, half the escape speed of earth , then the maximum height attained by it is [R is radius of earth]

Joshi sir comment

from ground to that point

1/2 m[√(2gR)/2] + [-GMm/R]  =  0 + [-GMm/(R+h)]

solve for h

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

Two point masses having mass m and 2m are placed at distance d. The point on the line joining point masses, where gravitational field intensity is zero will be at distance

Joshi sir comment

let the point will be at a distance of x from m then compare the gravitational field of the two masses at that point

Physics >> Mechanics Part 2 >> Gravitation Medical Exam

If earth suddenly stop rotating, then the weight of an object of mass m at equator will [ ω is angular speed of earth and radius R is its radius]