unit 1

Question 1

what is necessary to keep an object in circular motion

Answer 1

centripetal force

Question 2

what causes a change in the angular (rotational)
motion of an object.

Answer 2

an unbalanced torque

Question 3

whats the moment of inertia of an object

Answer 3

a measure of its resistance to angular
acceleration about a given axis.

Question 4

what does the moment of inertia depend on

Answer 4

mass and the distribution of mass about
a given axis of rotation.

Question 5

whats conversation of momentum

Answer 5

the momentum before equals the momentum after a collision in the absence of external torques

Question 6

whats gravitational field strength

Answer 6

as the gravitational force acting on a unit mass

Question 7

whats gravitational potentail of a point in space

Answer 7

the work done in moving
unit mass from infinity to that point.

Question 8

whats escape velocity

Answer 8

as the minimum velocity required to allow a mass to
escape a gravitational field to infinity, where the mass achieves zero kinetic energy and
maximum (zero) potential energy.

Question 9

inertial?

Answer 9

non-accelerating

Question 10

whats the equivalence principle

Answer 10

it is not possible to distinguish between the
effects on an observer of a uniform gravitational field and of a constant acceleration

Question 11

whats spacetime

Answer 11

a unified representation of three dimensions of space
and one dimension of time.

Question 12

general relativity leads to the interpretation that

Answer 12

mass curves
spacetime, and that gravity arises from the curvature of spacetime.

Question 13

whats geodesic

Answer 13

the path with the
shortest distance between two points

Question 14

escape velocity from the event horizon of a black hole is equal to

Answer 14

speed of light

Question 15

from the perspective of a distant observer, time appears to be frozen
at

Answer 15

the event horizion of a black hole

Question 16

whats schwarzchild radius

Answer 16

is the distance from its centre
(singularity) to its event horizon.

Question 17

how are stars formed

Answer 17

stars are formed in interstellar clouds when gravitational forces
overcome thermal pressure and cause a molecular cloud to contract until the core
becomes hot enough to sustain nuclear fusion, which then provides a thermal pressure
that balances the gravitational force

Question 18

give an exmaple of propton-protn chain

Question 19

what are the classifications of h-r diagrams

Answer 19

main sequence, giant, supergiant and white dwarf

Question 20

where does fusion of hydrogen occurs in the core of stars

Answer 20

main sequence

Question 21

what happens at the end of a stars life

Answer 21

. When the
hydrogen in the core becomes depleted, nuclear fusion in the core ceases. The gas
surrounding the core, however, will still contain hydrogen. Gravitational forces cause both
the core, and the surrounding shell of hydrogen to shrink. In a star like the Sun, the
hydrogen shell becomes hot enough for hydrogen fusion in the shell of the star. This leads
to an increase in pressure which pushes the surface of the star outwards, causing it to
cool. At this stage, the star will be in the giant or supergiant regions of a HertzspungRussell (H-R) diagram.

Question 22

what determines a stars lifetime

Answer 22

mass

Question 23

what will every star eventually become

Answer 23

a white dwarf, a neutron star or a black
hole.

Question 24

what will happen to the sun

Answer 24

the core shrinks and will become hot enough for the
helium in the core to begin fusion.