PHYSICS ENTRANCE 2015 – SMART ETHIO E-Learning

Welcome to your PHYSICS ENTRANCE 2015

Choose base has one more hydrogen and D one fewer minus charge than the corresponding base.

1.

Which one of the following units is NOT a possible unit of electric field strength?

Volt/meter

Joule /(Coulomb x meter)

Newton/Coulomb

Joule / Coulomb

2.

Which one of the following statements does NOT describe magnetic nature of a material?

There is no a single magnetic North or magnetic South Pole

Magnetic dipoles of a material aligned parallel when the magnetic material is placed in external magnetic field.

Magnetic molecules (dipoles) are oriented randomly when a material lose its magnetism.

Magnetic molecules in a magnet will align when they are heated or hammered.

3.

Which one of the following statements is correct about conduction in semiconductors?

When atoms with half-filled electrons are doped with atoms of five valance electrons, the majority charge carriers are holes.

The majority charge carriers in N-type semiconductors are electrons due to doping.

N-type semiconductor is made from half-filled shell atoms doped with accepter atoms.

P-type semiconductors have holes as minority charge carriers in the crystal lattice of the material.

4.

A small source emits sound wave measured and waves which are spherical. The intensity of the At what distance from the source would the inter the source is 1=5 W/m². as it is at r=3.0 m ?

6.0 m

9. m

4.5 m

12.m

5.

Consider a system of two point masses M₁and M₂. with M₁=0.5M₂The two masses are located on the X-Y plane as shown in the figure below.

Which one of the following alternatives indicates the position of center of mass of the system?

6.

What is the acceleration due to gravity at an altitude twice the radius of the Earth? ( g_E is the gravitational acceleration on the surface of the Earth).

7.

flour capacitors are connected in a capacitor network as shown in the figure below.

The equivalent capacitance between terminals a and b in μF is

3/4

1/4

4

12

8.

A 64 V battery is connected to a series combination of 3kΩ bulb and 4kΩ electric iron. If the total current in the circuit is 8 mA , what is the internal resistance of the battery?

1KΩ

7KΩ

8KΩ

15KΩ

9.

A solenoid with 5000 turns and length 1 m carries 15 A of current. If no iron core is inserted in the solenoid, what is the magnetic field strength at the center of the solenoid?

4π x 10^-2T

20π x 10^-2T

6π x 10^-2T

3π x 10^-2T

10.

Light ray is allowed to enter from air medium ( n_ait=1 ) into water medium (inex of refraction n_w=4/3 ) at an angle of 30º with the normal to air-water interface (boundary). Which one of the following is correct about the ray of light?

The sine of the angle of refraction of the light ray in water is equal to 0.5 .

The speed of the light ray in water is 1.33 times that of its speed in air.

The sine of the angle of refraction of the light ray in water is equal to 0.38 .

The speed of the light ray in water is 0.9 times that of its speed in air.

11.

A fluid travelling over an objects surface exerts less pressure than if the fluid was static. This is a statement of

Pascal's principle.

Archimedes' principle.

principle of continuity.

Bemoulli's principle.

12.

Which one of the following activities of experiment is NOT necessary to determine the specific latent heat of vaporization of water?

Measuring volume

Measuring time

Measuring mass

Measuring temperature

13.

Which one of the following statements is correct about critical and boiling points of a substance?

The critical point and the boiling point of a substance occur at the same specific temperature and pressure.

The critical temperature of a substance can be increased or decreased based on the pressure of the surrounding whereas boiling point does not vary with the pressure of the surrounding.

The boiling point of a substance can be different based on the pressure of the surrounding whereas critical point occurs at one specific pressure and temperature.

Both critical temperature and boiling point of a substance can be increased or decreased based on the pressure of the surrounding.

14.

A 30 kg rigid object has a moment of inertia
45 kg m²about its center of mass. What is the object's moment of inertia when it rotates through an axis 2 m a way and parallel to the axis through its center of mass?

165kg m²

105kg m²

90 kg m²

180kg m²

15.

Two coplanar forces acts on a uniform beam as shown in the figure below.

the moment of force on the beam is

24.0 Nm

30.0 Nm

48.0 Nm

12.0 Nm

16.

Water flows at the rate of 500.0 cm³/s at small cross-section 5 cm². The larger cross-section is 25 cm². What is the ratio of the speed of the water at A₁ to A₂.

100

0.2

20

5

17.

An ideal monoatomic gas expands adiabatically from an initial volume of 2 liters at a temperature of 300 K to 16 liters of volume. What is the final temperature of the gas? (Use the ratio of specific heat capacity at constant pressure to that at constant volume to be 5/3.)

75 k

37.5 k

1200 k

2400 k

18.

Consider a particle performing a circular motion around a circle of radius r, with an angular velocity w and the particle's projection on the horizontal diameter of the
circle (between points Q and R ) as shown in
the figure below?

Which one of the following statements is correct about the motion of the particle and its projection on QR

The circular motion of the particle can be taken as a simple harmonic motion.

The projection of the particle on QR swings between points Q and R with constant speed.

The projection of the particle on QR demonstrates simple harmonic motion.

The projection of the particle on QA demonstrates motion with constant acceleration.

19.

Air molecules vibrate in a pipe of length L closed at one end but open at the other. If the speed of sound through the pipe is V, Which one of the following statements is correct about the resonance effects of vibration of air molecules in the pipe?

The resonance frequency of the first harmonics is V/L

The fundamental wave length of resonance is equal to 2 L .

The fundamental resonance frequency V/4L

The wavelength of the third harmonic is equal to L.

20.

A monochromatic light of wave length λ passes through double slits separated by a distance d. If the path difference between the lights is P and n being an integer
(0, 1, 2, 3, . . ), Which one of the following
would be observed on screen behind the
slits

constructive interference if p=nλ

constructive interference if p=(n+1/2)λ

destructive interference if p=0

destructive interference if p=2πλ

21.

Suppose you are standing on a horizontal floor, in a room, with one of your feet and leaning the wall of the room with the other foot. The number of action reaction pair of forces you experience is

2

3

4

1

22.

The amount of heat energy required to change a substance from a liquid to a gaseous state is known as

quantity of heat.

latent heat of fusion.

specific heat capacity.

latent heat of vaporization.

23.

Which one of the following is correct about mechanical waves?

The time taken for one complete wave to pass a given point is called the frequency of the wave.

The distance between two identical points on adjacent waves is known as the wavelength of the wave.

The number of complete waves that passes a given point per time is called the period of the wave.

The maximum height in a transverse wave is known as the trough of the wave.

24.

A boy in a journey covers his route by travelling 3.0 km east and 4.0 km north. What is the magnitude of his resultant displacement?

7.0 km

2.7 km

1.0 km

5.0 km

25.

The graph given below shows the velocity of a man travelling on a motorcycle as a function of time.

Which one of the following statements is correct about the velocity-time graph?

The displacement during the time intervals
t=0 to t=6 s is equal to the area under the
velocity-time graph in the given interval.

The displacement during the time interval
from t=6 s to t=14 s is equal to the area of region II minus the area of region III.

The acceleration in the first 6 s is equal to
the gradient of the curve in the given
interval and it is positive.

The acceleration during the time interval from t=6 s to t=10 s is equal to the gradient
of the curve in the given interval and it is negative.

26.

A car of mass 1.50 x 10³ kg collides with a wall and rebounds. The initial and final velocities of the car are v_i =15.0 m's and v_f =2.60m/s, respectively. If the collision lasts for 0.15 s , what is the magnitude of the average force exerted on the car?

1.76 x 10⁵ N

2.64 x 10⁴ N

3.96 x 10³ N

2.60x 10⁴ N

27.

Starting from rest, a block of mass 5.0 kg slides 2.5 m down a rough 37° incline. The coefficient of kinetic friction between the block and the incline is μ_k=0.44. What is the work done by the friction force on block?

-75.00 J

-44.00 J

-18.92 J

-59.00 J

28.

An inclined plane is 20 m long and is inclined at an angle of 15° to the horizontal. If the effort required to push a block of weight 3, 000 N up the slope is 900 N , what is the efficiency of the inclined plane?

25.9%

30.0%

100%

86.7%

29.

A wooden block of volume 5.00 x 10^-4 m³ floats partially submerged in water, and a small steel object of mass m is placed on top of the block. When m=0.25 kg, the system is ln equilibrium and the top of the wooden block is at the level of the water. What is the density of the wood?

1500 kg m^-3

1000 kg m^-3

500 kg m^-3

800 kg m^-3

30.

A bimetallic strip made up of iron and brass bonded together is used in a thermostat. The coefficient of linear expansions for iron and brass are 1.1 x 10^-5 /K and 1.9 x 10^-5 /K, respectively. Which of one the following phenomena occurs when the temperature changes?

When the temperature increases, the brass section of the bimetallic strip expands faster than the iron and the strip bends towards the iron section.

When the temperature increases, the iron section of the bimetallic strip expands faster than the brass and the strip bends towards the brass section

When the temperature decreases, the iron section of the bimetallic strip contracts faster than the brass and the strip bends towards the iron section.

When the temperature decreases, the brass section of the bimetallic strip contracts slowly than the iron and the strip bends towards the brass section.

31.

Which one of the following statements does NOT describe coherent light or interference of coherent light?

In order for two waves to be coherent, they must be the same type of wave.

Two waves which maintain constant phase relationship can produce sustained interference.

Sustainable interference pattern can be formed by two waves with variable phase difference.

Coherent light waves have the same frequency and wavelength.

32.

Kirchhoff's junction rule is a consequence of conservation of

charge

electrical energy.

mass

momentum

33.

Which one of the following statements describes the photoelectric effect interaction of radiation with matter?

The intensity of radiation incident on a material can affect the energy of photoelectrons emitted from the metal surface.

In photoelectric effect, the photoelectron energy is directly proportional to the wavelength of incident radiation.

Any value of energy of photons (radiations) is capable of producing photoelectrons from a metal.

When radiation of certain frequency ƒ, interact with atoms of a material, electrons will be emitted with energies proportional to the radiation energy.

34.

A positive point charge of 2μC is placed on the x-axis at the origin and a positive charge of 6μC and a negative point charge of —4μC are placed, respectively at x=-3 cm and x=+3cm on the x-axis. What is the net electric force on the 2μC charge?

200 N toward the negative x -axis

40 N toward the positive x -axis

40 N toward the negative x -axis

200 N toward the positive x -axis

35.

Consider a point charge Q in an electrostatic field and a point mass m in a gravitational field. Which one of the following statements is correct about the potential energy of the objects?

The potential energies at distance r , from the field sources for both Q and m vary inversely with r2.

The potential energy of the point charge and that of the point mass changes as they move over equipotential surfaces in their respective fields.

The electric potential decreases as a positive charge moves opposite to the electric field A while the gravitational potential of the mass increases when it moves along the gravitational field.

The gravitational force on mass is in the same direction of gravitational field while D electric force on Q in the same or opposite directions of electric field depending the sign of the charge.

36.

Four resistors are connected to a voltage source as shown in the circuit diagram shown below

What are the current through the 3Ω resistor and the voltage drop across the 4Ω resistor, respectively?

4/3 A and 8V

2 A and 3/4 V

3/4 A and 3/4 V

2/3 A and 4V

37.

An electron moving with a speed of 2.2x l0⁷ m/s east enters in the region of magnetic field strength of 5 x 10^-4 T directed north. What is the magnetic force experienced by the electron?

1.76 x 10^-15 N towards north direction

8 x 10^-15 N Perpendicular to north and east directions

3.64 X 10^-30N, towards east direction

1.76 x 10^-15 N, perpendicular to north and east directions

38.

A magnetic field intensity of 4 x 10^-4 T crosses a coil having face area 100 2 and 5 X 10⁴ turns perpendicular to the face of the coil. If the magnetic flux in the coil set to zero within 2 ms . What is the magnitude of the induced emf in the coil?

4 x10^-4V

2 x 10^-5V

10 V

100 V

39.

In a simple ac circuit, an inductor of 4pH and a capacitor of 9 pF are connected in series to each other and the combination is connected to an ac source. What is the angular frequency at resonance of the circuit?

3.8 x 10⁸ rad/s

3.6 x 10⁷ rad/s

1.67 x 10⁸ rad/s

2.7 x 10⁵ rad/s

40.

40 Electrons in a Sodium atom emit radiation when they move from a higher energy level of -0.81 eV to a lower energy level of -2.21 eV
What is the frequency of radiation emitted
in the process?

8.10 x 10¹⁵ Hz

3.38 x 10 ¹⁴Hz

1.40 x 10¹⁵ Hz

2.21 x 10¹⁴ Hz

41.

Which one of the following statements is NOT correct about power of a lens?

The larger the focal length of the lens the greater is the power of the lens.

The power of a lens is the measure of the strength of the lens.

Optician gives the name diopters for the unit of power of a lens.

The power of a lens decreases as the focal length of the lens increases.

42.

Which one of the following groups of physical quantities contains only vectors?

Momentum, Energy, Magnetic field and Force

Acceleration, Speed, Force and Electric field

Work, Electric field, Displacement and force

Displacement, Velocity, Magnetic field and Momentum

43.

Which rule about the number of significant figures is correct? Zeros in the number

1.1000 are not significant figures.

450.0 are significant figures.

0.0023 are significant figures.

2.70018 are not significant figures.

44.

Given two vectors v₁=10 units along the positive y-axis and v₂=6 units at an angle of 37º above the positive x-axis. What is the scalar product of the vectors in square of units?

45

48

36

60

45.

An airplane takes-off at airport A and travels 500 km due east within one hour and then turning to south it flies for 20 minutes to land on airport B which is 100 km away from the turning point. The magnitude average velocity of the plane during its flight between the two airports is

75V26km/h.

75√24 km/h.

450 km/h.

100√34km/h.

46.

46 A bullet is fired with an initial speed v at an angle 0 with the horizontal. It takes a time T to reach its maximum vertical displacement h_max . It hits the target point a distance fi away and exactly in the horizontal level to the point where it was fired. Which one of the following statement is NOT correct about the motion of the bullet?

θ should be different from 90° to hit the target at a distance R

h_{max is directly proportional to the initial
speed v}

The bullet hits the target at a time 2 T after was fired.

R will be maximum if cos θ=√2/2

47.

A man pushes a 25.0 kg object by 250 N force along an inclined plane inclined at an angle of 37º to the horizontal. If the object moves with constant speed, the friction force exerts on the block is

250.0 N, down the inclined plane

100.0 N, up the inclined plane

250.0 N, up the inclined plane

100.0 N, down the inclined plane

48.

The following three collisions occur in different systems.

I. A billiard ball A collides with an identical ball B and comes to rest after collision, while ball B moves with the same velocity as ball A was moving before.

II. A bullet moving with speed * hits a suspended mass and it imbedded in it and the combination moves with common velocity.

III. Two cars moving in opposite direction become at rest after collision.

Which of the following statements is correct about these collisions?

I and III are elastic collisions.

I, II and III are inelastic collisions.

II and III are inelastic collisions.

I and II are elastic collisions.

49.

An object of mass M is attached to a spring of spring constant N, as shown in the figure below.

If the mass is pulled to a point P, which is at distance A from equilibrium position O , and released, Which one of the following statements is correct about energy of the system? (assume the surface is frictionless)