Past Paper Mistakes (Paper 2)

Question 1

Explain why the driver’s reaction time affects the thinking distance of a car.

Answer 1

distance = speed × time

(so) longer reaction time =
longer distance

Question 2

A hailstone falls from a cloud and accelerates.

Why does the hailstone accelerate?

Answer 2

There is a resultant force acting.

Question 3

The hailstone stops accelerating and reaches terminal velocity.

Explain why the hailstone reaches terminal velocity.

Answer 3

as the velocity of the hailstone
increases air resistance
increases

until air resistance becomes
equal to the weight of the
hailstone

so the resultant force is (equal
to) zero

Question 4

Explain the difference in the maximum kinetic energy of a hailstone with a mass of 10 g and a hailstone with a mass of 20 g.

Answer 4

kinetic energy depends on both
mass and velocity

as mass increases so does
terminal / maximum velocity

kinetic energy ∝ m and kinetic
energy ∝ v2 so as mass doubles
kinetic energy more than
doubles

Question 5

What is meant by ‘centre of mass’?

Answer 5

The point where the mass
appears to be concentrated.

Question 6

Compare the formation and life cycles of stars with a similar mass to the Sun to stars with a much greater mass than the Sun.

Answer 6

all stars:

• form in a cloud of gas and dust (nebula) by gravity – mostly
  hydrogen
• forms a protostar
• fusion begins
• fusion of small nuclei into larger nuclei (hydrogen into
  helium)
• main sequence star – stable period where gravitational forces (inwards) balance forces (outwards) due to fusion
  processes.

comparisons:

• stars about the same size as the Sun expand to become a red giant, stars much bigger than the Sun expand to become
  a red super giant.
• stars about the same size as the Sun contract (and
  temperature increases) to become a white dwarf, stars much bigger than the Sun explode in a supernova.
• stars about the same size as the Sun (cool to) become a black dwarf, stars much bigger than the Sun become either a
  neutron star or black hole.

Question 7

Answer 7

A primary coil

B secondary coil

C iron core

Question 8

The input pd causes an alternating current.

Explain why there is an alternating current in the output when the transformer is
connected to a circuit.

Answer 8

(the alternating current causes)
a changing magnetic field
around the primary (coil)

creates magnetic field that
changes direction in the core

this induces an alternating
potential difference across the
secondary (coil causing an
alternating current)

Question 9

Swimmers practise diving to the bottom of the swimming pool to pick up the
diving brick.

Explain why the forces on the brick at the bottom of the pool cause the brick to be
stationary.

Answer 9

Upthrust acts (upwards on the brick)

Normal contact force acts
upwards (on the brick)

Weight is equal to upthrust plus normal contact force.