Question 1

The force *F *between two point charges *q*1 and *q*2, a distance *r *apart, is given by the equation

where *k *is a constant.

What are the SI base units of *k *? {Cambridge A level oct/nov 2016, ques 2, p11}

Solution

The SI base unit of force is Kgms-2

Charge* q*1 is As

Charge q2 is As

distance r is m

SI base unit of k = (Kgms-2 x m) / (As x As) = Kgm2s-4A-2 (B is the correct option)

Question 2

A student uses a cathode-ray oscilloscope (c.r.o.) to measure the period of a signal. She sets the time-base of the c.r.o. to 5 ms cm–1 and observes the trace illustrated below. The trace has a length of 10.0 cm.

What is the period of the signal? {Cambridge A level oct/nov 2016, ques 5, p11}

Solution

From the graph there are 3.5 oscillations

The distance to cover one oscillations = 10/3.5 cm

Since the time-base of the c.r.o is 5 ms cm–1

The period of the signal = (10/3.5) x 5 = 14.3 ms = 1.4 x 10-2 s (D is the correct option)

Question 3

A cyclist pedals along a raised horizontal track. At the end of the track, he travels horizontally into the air and onto a track that is vertically 2.0 m lower.

The cyclist travels a horizontal distance of 6.0 m in the air. Air resistance is negligible.

What is the horizontal velocity *v *of the cyclist at the end of the higher track? {Cambridge A level oct/nov 2016, ques 6, p11}

Solution

There are important points to note in this question:

The horizontal velocity v is used to calculate the horizontal distance

The time to reach the maximum height is the time to travel the horizontal distance

At maximum height u = 0

Using H = ut + 1/2gt2

2 = 0 + 1/2×9.81xt2

(t=0.6395s)

Horizontal distance = horizontal velocity(v) x time(t)

6 = 0.6395v

V = 9.4ms-2 (B is the correct option)

Question 4

A car is travelling at constant velocity. At time *t *= 0, the driver of the car sees an obstacle in the

road and then brakes to a halt. The graph shows the variation with *t *of the velocity of the car.

How far does the car travel in the 5.0 s after the driver sees the obstacle? {Cambridge A level oct/nov 2016, ques 8, p11}

Solution

The distance travelled by the car = 20 x 0.8 + ½ x 20 x(5 – 0.8) =16 +42 = 58m (C is the correct option)

Question 5

A car has mass *m*. A person needs to push the car with force *F *in order to give the car acceleration *a*. The person needs to push the car with force 2*F *in order to give the car acceleration 3*a*.

Which expression gives the constant resistive force opposing the motion of the car? {Cambridge A level oct/nov 2016, ques 11, p11}

Solution

Resultant force = applied force – resistive force

Ma = F- R

R = F- ma —-i

3ma = 2F – R

R = 2F – 3ma —–ii

Substitute for R in eq i

2F – 3ma = F – ma

F = 2ma

Therefore, R = 2ma – ma = ma

Resistive force = ma (A is the correct option)

Recommended: Solutions to Cambridge A level May/June Paper 1 Physics questions 2015 and 2016

Question 6

A car travels at a constant speed of 25 m s–1 up a slope. The wheels driven by the engine exert a forward force of 3000 N. There is a drag force due to air resistance and friction of 2100 N. The

weight of the car has a component down the slope of 900 N.

What is the rate at which thermal energy is dissipated? {Cambridge A level oct/nov 2016, ques 20, p12}

Solution

Rate at which thermal energy is dissipated = power loss

Power = force x velocity

Rate at which thermal energy is dissipated = drag force x velocity = 25 x 2100 = 5.3 x 104 W (C is the correct option)

Question 7

Two parallel circular metal plates X and Y, each of diameter 18 cm, have a separation of 9.0 cm. A potential difference of 9.0 V is applied between them.

Point P is 6.0 cm from the surface of plate X and 3.0 cm from the surface of plate Y.

What is the electric field strength at P? {Cambridge A level oct/nov 2016, ques 30, p12}

Solution

The kind of field in this this is a uniform electric field. Therefore, at any point in the field the electric field strength is constant.

Electric field strength = potential difference / distance between the plate = 9 / 0.09

Electric field strength at P = 100 Nc-1 (B is the correct option)