Kepler's laws of planetary motion — NEET & JEE Questions

Question 1 · difficulty L1 · recall

According to Kepler's first law, planets move around the Sun in

• A. elliptical orbits with the Sun at one focus
• B. circular orbits with the Sun at the centre
• C. parabolic orbits with the Sun at the vertex
• D. straight lines

Question 2 · difficulty L2 · understanding

Kepler's second law states that the line joining a planet and the Sun

• A. sweeps equal areas in equal times
• B. has constant length
• C. rotates with constant angular speed
• D. sweeps equal angles in equal times

Question 3 · difficulty L2 · understanding

According to Kepler's third law, for planets orbiting the same central body

• A. $T^2\propto r^3$
• B. $T\propto r$
• C. $T^3\propto r^2$
• D. $T^2\propto r$

Question 4 · difficulty L2 · understanding

A planet moves faster in its orbit when it is

• A. closer to the Sun
• B. farther from the Sun
• C. at the same speed everywhere
• D. at either focus

Question 5 · difficulty L3 · application

A planet has orbital radius four times that of another planet around the same star. What is the ratio of their orbital periods?

• A. 2
• B. 4
• C. 8
• D. 16

Question 6 · difficulty L3 · application

A planet has an orbital period of 8 years around a star. If another planet orbits the same star with a semi-major axis four times smaller, what is its period?

• A. 1 year
• B. 2 years
• C. 4 years
• D. 6 years

Question 7 · difficulty L3 · application

A planet sweeps an area $A$ in 20 days at one part of its orbit. How much area does it sweep in the next 20 days?

• A. $A/2$
• B. $A$
• C. $2A$
• D. It depends only on its distance from the Sun

Question 8 · difficulty L3 · application

If the semi-major axis of a planet's orbit is increased by a factor of 9, by what factor does its period increase?

• A. 9
• B. 18
• C. 27
• D. 81

Question 9 · difficulty L4 · application

A planet is at perihelion and later at aphelion. Which statement is correct?

• A. Its speed is greater at perihelion than at aphelion
• B. Its speed is the same at both points
• C. Its speed is zero at perihelion
• D. Its angular momentum about the Sun is greater at perihelion

Question 10 · difficulty L4 · application

Two planets orbit the same star with periods 1 year and 27 years. What is the ratio of their semi-major axes $a_2/a_1$?

• A. 3
• B. 6
• C. 9
• D. 27