Download Geometry Questions

Problem Set – Inverse Square Law/Gravity & Light
Nov. 2011


:
The force due to gravity decreases as the square of the distance from the source.
The force due to gravity is proportional to the product of the two masses
Force = g 
GMm
r2
acceleration = a 
GM
r2
The Inverse Square Law for Light
 A "standard candle" is a star whose luminosity is known.
 The brightness of a star depends on its distance. Its brightness decreases as 1/d2. A
star of the same luminosity that is twice as far away will be ¼ as bright.
Gravity Questions
1. What is the acceleration due to gravity on the surface of a white dwarf? Let the mass
of a white dwarf by approximately 1 solar mass, or 2.0 x 1030 kg, and its radius be
approximately that of Earth or 6.4 x 106 m. (J63)
2. What is the acceleration due to gravity on the surface of a neutron star? Let the mass
of a neutron star be two solar masses or 4 x 1030 kg and its radius be 10 km. (J64)
Inverse Square Law
If two stars have the same intrinsic luminosity, but star A is ten times further away than
star B, how much fainter than star B will star A appear to be?
Answer Key – Gravity Problems
Gravity Questions
1. 3.2 x 106 m/s2 (J63)
2. 2.7 x 1012 m/s2 (J64)