# A-level Physics (Advancing Physics)/Gravitational Fields/Worked Solutions

G = 6.67 x 10^{−11} m^{3}kg^{−1}s^{−2}

**1. A 15 kg object has a weight of 8000N. What is the gravitational field strength at this point?**

**2. Draw a graph of gravitational field strength against distance.**

Since gravitational field strength is proportional to gravitational force, the two graphs look very similar.

**3. What is the gravitational field strength of the Sun (mass 2 x 10 ^{30}kg) on the Earth (mass 6 x 10^{24}kg, mean orbital radius 15 x 10^{10}m)?**

**4. What is the difference in the acceleration due to gravity over a vertical distance d?**

**5. How far would one have to travel upwards from the Earth's surface to notice a 1Nkg ^{−1} difference in gravitational field? (The Earth has a radius of 6400 km.)**

Using the quadratic formula:

Which is very horrible. If you plug in the numbers, you get:

Since we want a negative d (because of the minus sign we ignored right at the beginning):

Although, I have to confess, there was so much scope for error that it is almost certain that this is the wrong answer. If you fancy wading through and checking, feel free!

__[*] Solution :__

g'=g-1=9.8-1=8.8N/kg
g=GM/(R+d)^2
=>

d=349.96 km