| Finding g for an
unknown planet If an unknown planet
has 1/2 the radius and twice the mass, what is the value of g on the
planet.
g
unknown = (2
/ (1/2)2 )(g
Earth)
= 8 (g Earth)
Explanation: The above comes directly from
the universal gravity equation. Gravity force is directly proportional
to mass and inversely proportional to the square of the distance
between the centers of mass of the objects |
|
Angular
or rotational motion kinematics A fan
is switched on. It has an angular acceleration of 10 rad/s2.
After 10 seconds, what is the fan's angular velocity and displacement?
w = at
+ wo
= (10 rad/s2)(10 s) + 0
= 100 rad/s
q = 1/2 at2 + wot
= 1/2 (10 rad/s2)(10 s)2
+ 0
= 500 radians
|
| Elliptical Orbits
For an elliptical orbit of a mass =m around a
planet, the velocity at the closest point = vc and the
closest distance = Rc with the furthest distance = Rf.
What is the kinetic energy at the furthest distance?
First find the velocity vf
vf = (Rc/ Rf) vc
K = 1/2 m v 2
= 1/2 m [(Rc/ Rf)
vc] 2 |
|
Pendulums A pendulum with a mass of m
and length of L swings with a frequency of 3 Hz. What will the
frequency be for a pendulum with a mass of 3m and a length of 1/4 L?
f = 1/(2p) (g / L)^0.5
= 1/(2p)
[g / (1/4 L)]^0.5
= 1/(2p)
[4 g / L]^0.5
=
(2) 1/(2p)
[g / L]^0.5
but 1/(2p)
[g / L]^0.5 = original f, therefore
f =
2 (3 Hz)
= 6 Hz |