Dynamics and Space

Question 1

State what is meant by the term escape velocity:

Answer 1

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 2

A stone is stuck in the rim of a wheel. The angular vel of the wheel increase until the stone flies off. Explain in terms of forces why the stone flies off the rim.

Answer 2

The angular velocity increases so the required centripetal force increases

until the friction is insufficient (to hold the stone in place)

Question 3

State what is meant by moment of inertia.

Answer 3

A measure of an objects resistance to angular acceleration about an axis.

Question 4

Explain why systematic uncertainties occur.

Answer 4

Scale reading uncertainties are an indication of how precisely an instrument scale can be read.

Question 5

State what is meant by gravitational field strength.

Answer 5

The gravitational force exerted per unit mass.

Question 6

State what is meant by a world line:

Answer 6

Line that represents an object on a spacetime diagram.

Question 7

What will a distance observer notice about time at the event horizon of a black hole?

Answer 7

Time will appear to be frozen.

Question 8

Explain what is meant by a calibration uncertainty.

Answer 8

Calibration uncertainty arises when there is a difference between a manufacturer’s claim for the accuracy of an instrument when compared with an approved standard.

Question 9

State what is meant by apparent brightness.

Answer 9

The brightness of a star as measured on
Earth.

Question 10

Explain what is meant by a non-inertial frame of reference.

Answer 10

Frames of reference that are accelerating (with respect to an inertial frame).

Question 11

State what is meant by the phrase gravitational lensing.

Answer 11

A distribution of matter (such as a cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer.

Question 12

Explain why electrons follow a curved path between parallel deflection plates.

Answer 12

The electrons travel with constant) horizontal velocity.

Electrons travel with (constant) vertical acceleration.

Question 13

A car is travelling around a circular track at a constant speed. Explain why it is accelerating.

Answer 13

The car’s direction/velocity is changing. OR
Unbalanced/centripetal/cen tral force acting on the car.

Question 14

Explain briefly what happens when the hydrogen in a star’s core is depleted.

Answer 14

Nuclear fusion in the core ceases.
Gravitational forces cause both the core & surrounding H shell to shrink.

In stars like the Sun, the H shell becomes hot enough for H fusion to begin.

-> thermal pressure increases & star expands and then cools forming a giant or supergiant

Question 15

Explain what is meant by a conservative field.

Answer 15

A conservative field is one where the work done by the force on a particle that moves through any round trip is zero i.e. energy is conserved.

Question 16

explain why changing to a pike position reduces a gymnast’s angular momentum.

Answer 16

Mass (is now distributed) closer to the axis of rotation

Question 17

State what is meant by angular velocity.

Answer 17

The rate of change of angular displacement.

Question 18

State what is meant by torque:

Answer 18

Turning effect of a force.

Question 19

What do scale uncertainties tell us about measuring instruments?

Answer 19

Systematic uncertainties when readings taken are either all too small or all too large. This can arise due to faulty measurement techniques or experimental
design.

Question 20

Explain what is meant by gravitational potential.

Answer 20

The work done moving a unit mass from infinity to a point.

Question 21

State what is meant by a geodesic.

Answer 21

The shortest distance between two points in curved spacetime.

Question 22

What causes random uncertainties?

Answer 22

They arises when measurements are repeated, and slight variations occur. Random uncertainty may be reduced by increasing the number of repeated measurements.

Question 23

State the escape velocity from the event horizon of a black hole.

Answer 23

Speed of light in a vacuum.

Question 24

State what is meant by conservation of angular momentum.

Answer 24

Total angular momentum before an event is equal to the total angular momentum after an event in the absence of external torques.

Question 25

State what is meant by luminosity.

Answer 25

The energy emitted per second by a star.

Question 26

State what determines a star’s lifetime.

Answer 26

The star’s mass

Question 27

Explain briefly how stars are formed.

Answer 27

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 28

Explain the difference between accuracy and precision.

Answer 28

Accuracy compares how close the measurement is to the ‘true’ or accepted value. The uncertainty in a measurement gives an indication of the precision of the measurement.

Question 29

State the meaning of the term equivalence principle.

Answer 29

It is not possible to distinguish between the effects (on a body) of (uniform) acceleration and a (uniform) gravitational field.

Question 30

State the change that will occur in the fusion reactions within the core of the Sun at the point when it leaves the main sequence.

Answer 30

Fusion (of hydrogen) (in core) stops.

Question 31

Explain, in terms of gravitational force and thermal pressure, why the diameter of the Sun will increase as it becomes a red giant.

Answer 31

Outward forces caused by thermal pressure exceed gravitational
forces.

Question 32

State what is meant by
Spacetime.

Answer 32

Unified representation of 3D space and 1D time.

Question 33

State what is meant by the term Schwarzschild
Radius.

Answer 33

The distance from the centre of a black hole (singularity) to the event horizon.