The moon has a mass of 7.4 × 1022 kg and
completes an orbit of radius 3.8×108 m about
every 28 days. The Earth has a mass of
6 × 1024 kg and completes an orbit of radius
1.5 × 1011 m every year.
What is the speed of the Moon in its orbit?
Answer in units of m/s.


What is the kinetic energy of the Moon in
orbit?
Answer in units of J.


What is the kinetic energy of the Earth?
Answer in units of J.

Nhatkiem

velocity is distance per time

v=d/t

The distance the moon travels is the circumference of the circle it makes

d=c=2*pi*r
d= 2*pi*3.8×10^8m
d= 2.39*10^9 meters

time is given as 28 days, we need to convert it to seconds.

28 days *24 hours/day * 60 mins/hour * 60sec/min = 2419200 seconds

v= d/t = 2.39*10^9/2419200 seconds
v= 987 m/s

part two asks for the moons kinetic energy (K.E.)

KE = (1/2)*m*v^2 , where m is the mass of the object, and v is the speed it is traveling at.

KE = 0.5*7.4 × 10^22*(987)^2
KE = 3.60*10^28 Joules

Part three is similar to this, see if you can complete it from here.