Our Dynamic Universe

Question 1

Key area: Equations and graphs:

If the line in a velocity-time graph crosses the x-axis, what does this represent?

Answer 1

The object changes direction.

Question 2

Key area: Equations and graphs:

Why does the velocity-time graph of a bouncing ball diminish to zero as the ball bounces?

Answer 2

Energy is transferred to other forms during its journey.

Question 3

Key area: Equations and graphs:

In a displacement-time graph, what does the gradient represent?

Answer 3

Velocity

Question 4

Key area: Equations and graphs:

In a velocity-time graph, what does the gradient represent?

Answer 4

Acceleration

Question 5

Key area: Equations and graphs:

When considering velocity or acceleration in opposite directions (left/right, up/down), what must be given to the values?

Answer 5

Values must be assigned a positive or negative value e.g. down (-), up (+) or left (-), right (+) The + and - directions must be kept consistent throughout the problem.

Question 6

Key area: Forces, energy and power

When considering the acceleration of a rocket, what forces must be taken into consideration?

Answer 6

Thrust (upwards) Weight (downwards)

Question 7

Key area: Forces, energy and power

What causes an object to reach its terminal velocity?

Answer 7

The forces become balanced, therefore the object cannot accelerate any more.

Question 8

Key area: Forces, energy and power

What three things could cause the acceleration of a rocket headings towards space to increase?

Answer 8

Reducing mass due to consumption of fuel. Reducing air friction as the rocket moves further from the Earth’s surface. Reducing influence of gravity as the rocket moves away from Earth.

Question 9

Key area: Forces, energy and power

If an object is struck with a diagonal path into the air, what must be done to analyse its motion?

Answer 9

The diagonal path must be resolved into horizontal and vertical components of the motion of that object.

Question 10

Key area: Forces, energy and power

If an object has 200J of gravitational potential energy at the top of a slope and has 180J of kinetic energy once it has rolled down the slope, what has happened to the missing 20J?

Answer 10

Potential energy has been converted into forms other than kinetic, such as heat and sound energy.

Question 11

Key area: Forces, energy and power

Define friction

Answer 11

Friction is a force which opposes the motion of an object.

Question 12

Key area: Forces, energy and power

A block is being pulled along a surface by a force. There is friction between the block and the surface. What must be done before the motion of the block is analysed further?

Answer 12

The frictional force must be subtracted from the pulling force to find the resultant force.

Question 13

Key area: Collisions, explosions and impulse

State the law of momentum

Answer 13

For a collision occurring between object 1 and object 2, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision in the absence of any external forces.

Question 14

Key area: Collisions, explosions and impulse

In what situation is a collision elastic?

Answer 14

Where the total kinetic energy after the collision is equal to the total kinetic energy before.

Question 15

Key area: Collisions, explosions and impulse

In what situation is a collision in inelastic?

Answer 15

Where the total kinetic energy after the collision is less than the total kinetic energy before.

Question 16

Key area: Collisions, explosions and impulse

Using the relationship Ft = mv - mu to help explain, why does a crumple zone or airbag limit the injury to the occupant of a car?

Answer 16

The momentum of a car’s occupant will reduce significantly during a collision. Rearranging the equation for F shows that the longer the collision, the less the average force on the person.

Question 17

Key area: Collisions, explosions and impulse

If two balls of the same mass fall from the same height onto a force sensor, how would their force-time graphs compare if one was made of a solid material and the other was made of a flexible material?

Answer 17

The objects would have the same momentum before the collision as mass and speed are equal. On contact with the sensor, the force exerted by the flexible ball will be applied over a longer time. The graph of the hard ball would be tall and narrow, the graph of the softer ball would be short and wide but both would have the same area underneath them.

Question 18

Key area: Gravitation

Explain how a satellite orbits a planet or star.

Answer 18

Satellites are in constant freefall under the influence of the gravity of the object they are orbiting. The satellites must have sufficient horizontal velocity for it to continue in orbit where its motion can be considered as a projectile path.

Question 19

Key area: Gravitation

What can be said about the horizontal and vertical motion of a projectile?

Answer 19

Both horizontal and vertical motions are independent of each other.

Question 20

Key area: Gravitation

According to Newton’s Universal Law of Gravitation, what two things influence the force between two objects.

Answer 20

1) The mass of the two objects. 2) The distance between the two objects.

Question 21

Key area: Special Relativity

What can be said about the speed of light, regardless of a person’s frame of reference?

Answer 21

The speed of light is constant.

Question 22

Key area: Special Relativity

How does the measurement of time differ for a moving observer compared to a stationary observer?

Answer 22

Measurements of time for a moving observer are different compared to those for a stationary observer, giving rise to time dilation.

Question 23

Key area: Special Relativity

For a stationary observer how does the length of an object moving at speed compare to the length of the object at rest?

Answer 23

The moving object appears to be shorter.

Question 24

Key area: The Expanding Universe

As an object moves away from a stationary observer, what does this do to: a) the apparent colour of light it emits? b) any sound it may make?

Answer 24

a) Light from an object moving away will shift towards the red end of the spectrum (red shift). b) Sound being emitted by an object moving away from an observer will sound lower in pitch than the sound the object is emitting.

Question 25

Key area: The Expanding Universe

As an object moves towards a stationary observer, what does this do to: a) the apparent colour of light it emits? b) any sound it may make?

Answer 25

a) Light from an object moving away will shift towards the blue end of the spectrum (blue shift). b) Sound being emitted by an object moving towards an observer will sound higher in pitch than the sound the object is emitting.

Question 26

Key area: The Expanding Universe

Explain red shift

Answer 26

As an object moves away from the observer, there appears to be less waves observed in a given time, therefore the frequency of the light appears to reduce.

Question 27

Key area: The Expanding Universe

What does Hubble’s law (v = H_od) allow an estimation of?

Answer 27

The age of the Universe

Question 28

Key area: The Expanding Universe

What evidence exists to support the theory that the Universe is expanding?

Answer 28

Distant objects have been found to be accelerating away from us. ‘Dark energy’ is though to be responsible for providing the extra energy to make this happen.

Question 29

Key area: The Expanding Universe

How is it possible to estimate the mass of a galaxy?

Answer 29

The orbital speed of the stars within a galaxy provides enough information to estimate the mass contained within that galaxy.

Question 30

Key area: The Expanding Universe

Where does the theory of ‘dark matter’ come from?

Answer 30

By estimating the orbital speed of stars, the rates of rotation are too large for the mass which can be observed. A different type of matter, ‘dark matter’, is though to exist.

Question 31

Key area: The Expanding Universe

What information can be gathered from stars to determine their temperature?

Answer 31

The temperature of a star can be measured by observing the intensities of the different wavelengths of light emitted.

Question 32

Key area: The Expanding Universe

What evidence exists to support the theory of the Big Bang?

Answer 32

• Cosmic microwave background radiation (CMBR).
• The abundance of light elements such as hydrogen and helium.
• The darkness of the sky (Olber’s paradox).
• The large number of galaxies showing red shift rather than blue shift.

Question 33

Key area: Equations and graphs:

What is the difference between a scalar and vector quantity?

Answer 33

A scalar quantity has magnitude only. e.g. speed

A vector quantity has magnitude and direction. e.g. velocity