All: Paper 2

Question 1

Explain why the time to fall vertically between the plates (electric field) is independent of the mass of a particle.

Answer 1

-Force on a particle = mg and acceleration = F/m so always = g
-Time to fall (given distance) depends (only) on the distance and acceleration
OR:
-g = GM/r2
Time to fall = √2s/g
so no m in equations to determine time to fall

Question 2

State and explain two reasons, why the horizontal acceleration of a particle is
different for each particle (electric field).

Answer 2

• Mass is not constant since particle mass will vary
• Charge on a particle is not constant
• Acceleration = Eq/m or (V/d) (q/m) or Vq/dm
• E or V/d constant but charge and mass are ‘random’ variables so q/m will vary (or unlikely to be the same)

Question 3

State two assumptions made about the motion of the molecules in a gas in the
derivation of the kinetic theory of gases equation.

Answer 3

• The molecules (continually) move about in random motion
• Collisions of molecules with each other and with the walls are elastic
• Time in contact is small compared with time between collisions
• The molecules move in straight lines between collisions

Question 4

Use the kinetic theory of gases to explain why the pressure inside a football
increases when the temperature of the air inside it rises. Assume that the volume of the ball remains constant.

Answer 4

• Ideas of pressure = F/A and F = rate of change of momentum
• Mean KE/mean speed of air molecules increases
• More collisions with the inside surface of the football each second

Question 5

Describe two essential features of the orbit needed for the satellite to appear
geostationary.

Answer 5

• Equatorial orbit
• Moving west to east
• Period 24 hours

Question 6

The same satellite is moved into a higher orbit. Discuss, with reasons, how this affects the signal strength and contact time for the receiver at the South Pole

Answer 6

-Signal would be weaker (as distance it travels is greater)
-Energy spread over wider area/intensity decreases with
increase of distance
-Signal received for longer (each orbit)
-Beam width increases with satellite height/satellite moves at lower angular speed)