UCL CENTRE FOR LANGUAGES
& INTERNATIONAL EDUCATION (CLIE)

UPC Practice Entry Tests

Test: Physics 1

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1.	The following are five properties of an object. Which one of the properties is a vector quantity?

	mass
	potential energy
	angular momentum
	density
	moment of inertia
Incorrect. Remember that a vector is a mathematical object that has direction in space.

2.	A particle of weight 5 N is held in position by two light rope. One of the ropes makes an angle of 60^o with the upward vertical, the other is horizontal. What is the tension in the horizontal rope?

	1.25√3 N
	5 N
	5√3 N
	10 N
	10√3 N
Incorrect. Draw a free-body diagram of the particle.

3.	Which one of these properties can be expressed in Ns²m^-4?

	mass
	volume
	weight
	density
	surface area
Incorrect. You can use Newton's second law to convert one newton in base units.

4.	A metal cube has density 8 g/cm³ and mass 216 g. What is the length of one side of the cube?

	2 cm
	3 cm
	8 cm
	24 cm
	27 cm
Incorrect. First find the volume of the cube.

5.	A boy of mass 40 kg balances evenly on two stilts, each having an area of 8 cm² in contact with the ground. What is the pressure exerted on the ground by one stilt?

	50 N/cm²
	40 N/cm²
	25 N/cm²
	5 N/cm²
	2.5 N/cm²
Incorrect. Pressure is force per unit area.

6.	A ship is sailing slowly due east and a passenger is on the deck at point P. In the diagram, points A, B, C, D and E are marked on the deck. Towards which of these points should the passenger walk at a suitable speed in order to move due north?

	A
	B
	C
	D
	E
Incorrect. You may need to clarify your understanding of the concept of relative velocity.

7.	A car's tyres are inflated so that an area of 50 cm² of each tyre is in contact with the ground. If the mass of the car is 1600 kg and it is evenly distributed between the four tyres, what is the pressure the road exerts on each tyre?

	8 N/cm²
	32 N/cm²
	80 N/cm²
	160 N/cm²
	320 N/cm²
Incorrect. First calculate the force due to gravity on each tyre.

8.	An electric heater is rated 250 V, 1000 W. If electricity costs 7p per kWh what is the cost of running the heater for 5 hours?

	3.5p
	7p
	17.5p
	35p
	70p
Incorrect. It costs 7p to run a 1000 W appliance for one hour.

9.

Similar cells, ammeters and resistors are used in the circuit shown.

The cells and ammeters have negligible resistance. When one cell is connected in series with one ammeter and one resistor. the ammeter reading is 0.1 A.

What is the value of the current through ammeter A₁ in the circuit shown in the diagram?

	0.1 A
	0.2 A
	0.3 A
	0.4 A
	0.5 A
Incorrect. The potential difference across a resistor of resistance R through which a current I passes equals RI.

10.	In the circuit of Question 9, what is the value of the current passing through ammeter A₂?

	0.1 A
	0.2 A
	0.3 A
	0.4 A
	0.5 A
Incorrect. You will need to use Kirchhoff's laws.

11.

A student sits on a freely rotating stool holding two dumbbells. Initially, the student and stool rotate at an angular speed of 2.0 rad s⁻¹ with a total moment of inertia of 6.0 kg m². The student then pulls the dumbbells inward, reducing the total moment of inertia to 2.4 kg m².
Assuming negligible external torque, what is the student's new rotational kinetic energy equal to?

	30 J
	40J
	50 J
	60 J
	70 J
Incorrect. When there is no external torque, angular momentum is conserved.

12.	Two ideal springs (of spring constant k = 1.0 N cm^-1) are suspended vertically and in parallel (next to each other). If a load of 200 g is attached to their common end so that each spring stretches by the same amount, what is the stretch equal to ? (take g = 10 m/s²).

	0.5 cm
	1 cm
	2 cm
	4 cm
	8 cm
Incorrect. What is the spring constant of two identical springs in parallel?

13.

Two radioactive sources X and Y have half-lives of 4.8 hours and 8.0 hours respectively. Both decay directly to form only stable isotopes. The activity of a sample of the source X is 320 Bq, and the activity of a sample of the source Y is 480 Bq. The two samples are now combined.
What is the activity of the combination of X and Y 24 hours later?

	25 Bq
	50 Bq
	55 Bq
	70 Bq
	85 Bq
Incorrect. Note that an activity of 1 Bq is 1 decay per second.

14.	What is a particle with a mass of approximately 1 atomic mass unit and a charge of +1 called?

	an electron
	a gamma particle
	a positron
	a proton
	an alpha particle
Incorrect. A positron and a proton both have a charge of +1. Which one has a mass of approximately one atomic mass unit?

15.	The sketch shows the masses and positions of two moons relative to a planet X. The gravitational force between 4m and X is F₁. The gravitational force between m and X is F₂. Which one is the correct relationship between the two forces?

	F₁ = F₂
	F₁ = 2F₂
	F₂ = 2F₁
	F₂ = 4F₁
	F₁ = 4F₂
Incorrect. The gravitational interaction between two masses is proportional to the product of the two masses and inversely proportional to the square of the distance between them.

16.	In the qualifying lap for a motor racing Grand Prix, one driver completes the 1.8 km circuit in 40 seconds. The driver's average speed for the lap is:

	0.0045 ms^-1
	22 ms^-1
	40 ms^-1
	45 ms^-1
	72 ms^-1
Incorrect. Average speed is total distance travelled over total time taken.

17.

A pulse of frequency 100 kHz is emitted from an ultrasound scanner, and is reflected from a foetus 10 cm below the transmitter placed on the mother’s abdomen. The speed of sound within the mother’s body is 500 m s⁻¹.
How long after its emission from the scanner does it take for the pulse to reach the receiver which is adjacent to the transmitter?

	0.2 ms
	0.3 ms
	0.4 ms
	0.5 ms
	0.6 ms
Incorrect. Think about the total distance the ultrasound pulse travels.

18.	The velocity versus time graph below represents the motion of an object acted on by a constant force. Which option shows the correct values for the instantaneous speed after 3 seconds, and the average speed over the first 3 seconds of the motion?

	A
	B
	C
	D
	E
Incorrect. The acceleration is constant (i.e. the gradient of the graph) so the average speed is initial speed plus final speed divided by 2. The instantaneous speed is the speed on the y-axis at t = 3 s (i.e. 12 m/s).

19.	A motorcycle of mass 250 kg accelerates from rest to a speed of 30 m s^-1 in 6 seconds. The total forces opposing this motion equals 1500 N. The thrust produced by the car's engine is:

	250 N
	1250 N
	1500 N
	2750 N
	3000 N
Incorrect. You may want to revise Newton’s second law of motion that says the sum of all external forces exerted on a mass is proportional to the acceleration of that mass.

20.

Two trolleys of mass 1 kg and 0.8 kg, travelling towards each other on a linear air track, collide head-on. The 1 kg trolley is initially travelling at 2 ms^-1 towards the 0.8 kg trolley, which is travelling at 3 ms^-1.

If, after the collision, the 1 kg trolley returns along its original path at 0.5 ms^-1, the 0.8 kg trolley will have a velocity of:

	0.125 ms^-1to the left
	0.125 ms^-1 to the right
	0.5 ms^-1 to the left
	0.5 ms^-1 to the right
	5.375 ms^-1 to the right
Incorrect. Think of the conservation of momentum.

21.	Which one of the following statements about nuclear physics is true?

	The process of emission of a gamma ray from a nucleus is called nuclear fission.
	The half-life of a radioactive substance is half the time taken for its nuclei to decay.
	The number of neutrons in a nucleus is its atomic number (proton number) minus its mass number.
	When a nucleus emits a beta particle, there is no change in the number of particles it contains.
	When a nucleus emits an alpha particle, one of its neutrons becomes a proton plus an electron.
Incorrect. You may want to revise the characteristics of beta plus and beta minus decays.

22.	A constant current of 50 μA is used to charge a capacitor for 3 minutes. The potential difference across the capacitor at the end of this time is 6 V. The capacitance of the capacitor is:

	25 μF
	47 μF
	100 μF
	555 μF
	1500 μF
Incorrect. Apply the definitions of capacitance and electric current.

23.

A heavy block of stone rests on a rough, horizontal surface. The block is subject to a horizontal force that increases from zero at a constant rate. Assume that the coefficient of friction is greater than zero and that its value is independent of whether or not the block is moving.
What happens to the block of stone? (Assume air resistance is negligible.)

	It moves forwards immediately and accelerates forwards with a constant acceleration.
	It remains stationary at first and then accelerates forwards with a constant acceleration.
	It remains stationary at first and then accelerates forwards with an increasing acceleration.
	It moves forwards immediately with a constant velocity.
	It remains stationary at first and then moves forwards with a constant velocity.
Incorrect. Think about the friction force before and after the block starts moving.

24.	A ray of monochromatic light emerging from a parallel-sided block of glass into air strikes the top side at angles shown in the diagram. The refractive index of the material of the parallel-sided block ray is equal to:

	0.54
	0.68
	1.53
	1.71
	1.86
Incorrect. Remind yourself of Snell’s law of refraction.

25.	Photons of light resulting from the transition labelled B have a frequency: (You may assume Planck's constant h = 6.63 x 10^-34Js)

	equal to 8.17 x 10^-14Hz
	lower than those resulting from transitions A and C
	equal to 6.12 x 10¹⁴ Hz
	higher than that from transition C, but lower than that for transition A
	equal to 5.42 x 10^-19 Hz
Incorrect. The difference of atomic energy levels is proportional to the frequency of light that is absorbed or emitted.

26.	The gravitational potential difference between a point at the surface of a certain planet and a point 10 m above that surface is 4.0 J kg^-1. Assuming the gravitational field is uniform, the work done in moving a mass of 2.0 kg from the surface to a point 5.0 m above the surface is equal to:

	0.16 J
	1.0 J
	2.0 J
	4.0 J
	16 J
Incorrect. Recall the relation between gravitational potential and gravitational potential energy and consider that the field is uniform.

27.	Two long parallel wires X and Y carry currents of 3 A and 5 A, respectively. The force experienced per unit length by X is 5x10^-5 N to the right, as shown in the diagram. The force per unit length experienced by wire Y is:

	2x10^-5N to the left.
	3x10^-5N to the right.
	3x10^-5N to the left.
	5x10^-5N to the right.
	5x10^-5N to the left.
Incorrect. Use the formula for the magnetic force between two current carrying conductors and the left hand rule for the direction of the force.

28.

Monochromatic light of wavelength 600 nm is used in a spectrometer to illuminate a diffraction grating set normally to the collimator. The grating has 3x10⁵ lines per metre. The telescope is used to scan the field to one side of the straight-through position. Not counting the 'straight-through' image, the maximum number of diffracted images of the slit visible to the observer will be:

	2
	5
	8
	10
	11
Incorrect. The law of diffraction says that d sin(theta)=n*(wavelength).

29.

A ball is dropped from a height of 16 m on to a horizontal surface, and on each bounce loses 50% of its kinetic energy.

After which bounce will the maximum height of the rebound fall to less than 160 cm for the first time?

(Assume air resistance is negligible, and the only external force acting on the ball while not in contact with the surface is gravity.)

	4th
	5th
	6th
	7th
	8th
Incorrect. Just before each bounce, the ball's kinetic energy is equal to the gravitational potential energy it lost during the fall.

30.	An ideal gas is heated at constant volume until its pressure doubles. Which one of the following statements is correct?

	The mean speed of the molecules doubles.
	The number of molecules doubles.
	The mean square speed of the molecules doubles.
	The number of molecules per unit volume doubles.
	The root mean square speed of the molecules doubles.
Incorrect. Revise the ideal gas equation and the definitions of rms speed and average speed of molecules in an ideal gas.