Past Paper 2 Mistakes

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

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 6

(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 7

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 7

Upthrust acts (upwards on the brick)

Normal contact force acts
upwards (on the brick)

Weight is equal to upthrust plus normal contact force.

Question 8

Explain how the flexible bumper reduces the risk of injury to the people in the bumper car during the collision.

Answer 8

increases the time taken for the
collision to occur

(so) the rate of change of
momentum decreases

reducing the force (on the
people)

Question 9

In an emergency the driver needs to apply the brakes suddenly to stop the car quickly.

The driver of the car is distracted.

Explain why the distraction will increase the stopping distance.

Answer 9

stopping distance includes
thinking distance

there is an additional time
before the driver applies the
brakes.

(so) the thinking distance will
increase