Physics national exam 2014 – SMART ETHIO E-Learning

Welcome to your Physics national exam 2014

Choose the best answer from given alternatives
You may refer to the information given below
when you need to work on some of the questions.

1.

An object is placed 25.0 cm in front of a concave mirror having focal length of 10. 0 cm. The magnification of the mirror is

1.5

16.7

2.5

0.67

2.

Which of the following statements distinguishes between random and systematic errors?

Random error is biased, whereas systematic error does not show bias.

Systematic error makes measured values to be always above or always below the true value; whereas random error causes measured vales to be sometimes above and sometimes below the true value.

Systematic error can be minimized by taking several readings and averaging; whereas random error cannot be minimized.

Random error makes measured values to be always above or always below the true value; whereas systematic error causes measured values to be sometimes above and sometimes below the true value.

3.

The unit vector the direction

4.

Which of the following pair of vectors are collinear?

5.

For an object moving in straight line,

The slope of displacement-time graph and the area of the region under acceleration-time graph are, respectively, the acceleration and velocity of the object.

If the velocity increases by equal amount in equal time interval, the velocity -time graph is straight line with positive slope and the acceleration-time graph is horizontal.

The area of the region under the displacement-time graph and the slope of velocity-time graph are, respectively, the acceleration and displacement of the object.

If the displacement changes by equal amount in equal time interval, the displacement-time graph is horizontal line.

6.

Which of the following is true about satellite motion?

A satellite closer to Earth is faster than a satellite farther from the Earth.

for equal orbital radius, a satellite moving around the Earth has smaller speed than a satellite moving about moon.

A satellite moving closer to the Earth takes longer time to complete one revolution than a satellite farther from the Earth.

For two satellites moving around the Earth at equal orbital radius, a heavier satellite has larger speed than a lighter one.

7.

A block of mass m is placed on horizontal surface. The coefficient of static friction between the block and the surface is µ . A force of magnitude F acts on the block at an angle θ as shown in the figure below.

The minimum magnitude of the force F
required to slide the block on the surface is

8.

A ball of mass m moving with a speed v strikes a hard ball at an angle θ with the wall. It is reflected with the same speed at the same angle as shown in the figure below.

If the ball is in contact with the wall for time t
, then the average force acting on the wall is given by

9.

According to the work- energy theorem,

work done by gravity on an object thrown upward and moving upward is negative.

work done by gravity on an object downward is negative.

work done by gravitational force on a satellite moving around the earth m a circular is positive.

work done by tension on an object tied to a string and moving a horizontal circle is negative.

10.

Standing wave is formed when two identical waves travelling in opposite directions in the same medium interfere with each other. If y1 and y2 are the interfering waves and y= y1+ y2 is the resulting wave, which of the following in a circular is a correct combination?

11.

A young double slit experiment consists of two narrow slits separated by 0. 06 mm and 1.2 m away from a screen. If the slits are illuminated with a light of wavelength s63 » , the location of the fourth bright fringe on the screen is

4.5 cm

045 cm

3.94 cm

0.394 cm

12.

An electric dipole consists of a negative charge —q placed at a point with x and y coordinates (—2, — 2) and a positive charge +q at (2, 2). The dipole is placed in a uniform electric field directed i
n the positive x direction. If the dipole axis makes an angle θ

with the field, which of the following is true about the dipole?

It is in both translational and rotational equilibrium.

The field rotates the dipole in the direction of decreasing the angle 8, until the dipole becomes parallel to the field.

The field rotates it in the direction of increasing the angle 8, until the dipole is perpendicular to the filed.

It travels in the direction of the electric field.

13.

The electric potential at a distance of 2 cm from -1.6 change is

—14. 4 V

720 V

4 .4 V

— 720 V

14.

5 V

14 V

10 V

4V

15.

Consider a long and tightly wound solenoid length L and N tightly wound solenoid carrying current I, having length, which of the following describes the magnetic field produced by the solenoid?

The magnetic field inside the solenoid is constant and is parallel to the solenoid's axis, whereas the field outside is negligible.

The magnetic field inside the solenoid is uniform and perpendicular to the axis of the solenoid.

The magnetic field outside the solenoid is as strong as the field inside it.

The magnetic field inside the solenoid is zero, whereas the field outside is perpendicular to the length of the solenoid.

16.

According to the law of electromagnetic induction,

a changing magnetic field parallel to the plane of a circuit induces an emf in it.

an emf is induced in a circuit when a constant magnetic field crosses its surface.

the magnitude of emf induced in a circuit is directly proportional to the rate of change the magnetic flux crossing any surface bounded by the circuit.

a constant magnetic flux crossing the surface of a circuit induced an emf in the circuit.

17.

18.

According to the Heisenberg's uncertainty principle,

the more precisely we measure the position of a particle; we become less precise of its momentum and vice versa.

the larger the position uncertainty, the larger the momentum uncertainty.

if the uncertainty in position decreases, the momentum uncertainty decreases, too.

we can measure both the position and momentum of a particle simultaneously with unlimited precision.

19.

The graph of nuclear binding energy per nucleon (BE/A) versus mass number (A) has its peak near an atomic weight A—56. Which of the following statements is true about the graph?

energy per nucleon generally increases with the increase of mass number; indicating that lighter atoms can increase stability through nuclear fission.

For heavier nuclei (A > 56), the binding energy per nucleon decreases with the increase of mass number; implying that heavier atoms can increase their stability by increasing their proton's number.

Nucleus with larger number of neutron is more stable than nucleus of the same atom with smaller number of neutron.

Uranium (A=236), which has larger binding energy than iron (A=56), is more stable than iron.

20.

Which of the following statements is NOT correct about reflection and refraction of sound waves and their applications?

Reflection of sound (echo) is formed when sound enters a medium of varying densities.

Reflection and refraction of sound are used to detect flaws in metals and to help people park their cars.

Refraction of sound is the change in its direction as it travels through a medium having different densities.

In pre-natal scanning, reflection and refraction of sound allows doctors to monitor the progress of a developing batty.

21.

A torque T rotates an object of mass and moment of inertia I through an angle θ. The work done on the object by the torque is

22.

A satellite revolves around the earth in a circular orbit of radius =4 X 10^-16 The period of the satellite is

23.

One of the following statements is a correct description of the charging processes?

When a neutral metallic sphere is charged by induction using a negatively charged rod, the sphere acquires a net negative charge.

During charging a neutral object by induction using a negatively charged rod, charge flows from the rod to the object.

When a plastic rod is rubbed with wool, the two objects acquire a net charge of the same region.

When a positively charged object is momentarily brought into contact with a neutral metallic sphere, the sphere acquires a net positive charge.

24.

A parallel plate capacitor is charged with a battery. The battery is then disconnected, and a dielectric material is inserted between the plates of the capacitor. Which of the following is correct about the effect of the dielectric?

The potential difference between the plates remains the energy stored increases.

The capacitance remains the same and the electric field between the plates increases.

The electric field between the plates and the energy stored decrease.

The charge on the plates decreases and the energy stored increases.

25.

Which one of the following statements is correct about the resistance of a conductor with a circular cross-section?

The resistance of the conductor increases as its length and diameter increases.

The resistance of the conductor decreases as it is heated.

At a given temperature, the resistance of copper and silver wires of the same length and diameter is the same.

The resistance of the conductor increases as its length increases and its diameter decreases.

26.

A student wants to investigate Ohm’s law using an ammeter ( A ) and a voltmeter (V) to measure current through and potential difference across a resistor R. Moreover, she employs a rheostat to vary the potential difference across the resistor. Which of the following connections is the correct set up of the circuit to perform the experiment?

27.

Circular paths followed by two charges q1 and q2 moving the same speed in uniform magnetic field directed into the page (x) are shown in the figure below. If the two charges have the same mass, which of the following is correct about the sign and the magnitude of charges?

28.

The primary coil of a transformer has 250 turns and its secondary coil consists of 1500 turns. If 220 V is applied to its primary coil, the voltage induced in the secondary coil, respectively, are

1330 V and 6

1220 V and 60

1320 V and 60

1320 V and 6

29.

A diode is an electronic component that

allows electric current to pass through it in one direction.

allows the flow of current when its p-type region is connected to the negative terminal of a cell.

allows current to mass through it either from cathode to anode or from anode to cathode.

is useful to covert a DC voltage to AC voltage.

30.

Three forces, each having equal magnitudes of 10 N, are applied to an object on a horizontal A force F₁ makes an angle of 30⁰ above positive x—axis, F₂ makes 30⁰ above the negative x-axis, and the third Force F₃ _i_s directed along the positive x-axis.

The magnitude and direction of their resultant force are, respectively.

20 N450 above positive x—axis.

14. 1 N450 above positive x—axis.

20 N in the negative y-axis.

14 .1 N in the positive y-axis

31.

A student throws a ball vertica8y upward with a speed of 20 m/s, The maximum height reached by the ball and its velocity 30 s aft

15 m and 10 m/s downward.

20 m and 30 m/s upward

105 in and 50 m/s upward.

20 in and 10 m/s downward.

32.

Which one of the following statements describes the difference between different types of friction?

If there is a constant force applied to a stationary object on a horizontal surface, the static friction becomes equal to the limiting friction.

Limiting and kinetic frictions exist at the same time between two surfaces sliding over each other.

Limiting friction is the minimum value of static friction that keeps an object stationary.

for an object at rest on a horizontal surface, static friction increases with the increase of the applied force and reaches a maximum value just before sliding occurs.

33.

The apparent weight of a 60 kg student standing inside a lift is

720 N when the lift is at rest.

480 N when the lift accelerates downward with 2 m/s 2.

600 N when the lift accelerates with acceleration equal to gravitational acceleration.

600 N when the lift accelerates upward with 2 m/s

34.

Which of the following statements describe the use of energy resources?

Solar energy produced by photovoltaic cells in free of greenhouse gases and has a very low running cost.

Hydroelectric power generates a large amount of energy using small dam with little environmental impact and cheap initial cost of construction.

Wind energy, which is due to the pressure difference in space as the result of uneven sun heat, is a consistent and economical source of energy.

Geothermal energy is the most accessible, environmental friendly and inexpensive source of energy.

35.

A student wants to raise an object of mass m through a height h using an inclined plane that makes an angle θ above the horizontal. If I is the length of the inclined surface, which one of the following is correct about the actual mechanical advantage (AMA) and ideal mechanical advantage (IMA) of the inclined plane?

Neglecting frictions, its AMA is 1/ sin θ.

In the presence of friction, its AMA is 1/ sin θ

In the absence of friction, AMA is sin θ and its IMA is cos θ.

Neglecting fiction, its IMA is 1/ cos θ.

36.

According to the law of floatation, an object must displaces a volume of fluid

equals to its own weight.

equal to the weight of Un displaced fluid.

equal to its apparent weight.

less than its own weight.

37.

Which one of the following statements describes the unusual behavior of expansion of water?

As a temperature of water increases from 0°C to 4° C, its density increases since one molecule of water forms one hydrogen bond with another molecule

At O°C water has larger density and smaller volume than its density and volume at 4° C.

As a temperature of water increases above 4° C, its density increases since water molecules move further apart to form a second hydrogen bond with other molecules.

The density of water at 0° C is less than its density at 4° C, since water molecules move further apart and form a second hydrogen bond with other water molecules.

38.

A 40 g of water at 50° C is poured into a well-insulated 30 g of copper calorimeter at 20° C. The temperature of water at equilibrium becomes.

30° C

35° C

52.4°C

47. 9° C

39.

An FM radio signal is transmitted from a radio station at a frequency of 1.5 X 10⁸ H_z. If the wavelength of the radio wave is 2. 00 m, the speed of the FM signal is

40.

Which one of the following statements is correct about transformation of mechanical energy into other forms and the law of conservation of total energy?

Neglecting air resistance, an object moving vertically downward gains potential energy and loses an equal amount of kinetic energy.

Mechanical energy of a wooden block sliding on a rough horizontal surface is conserved.

Due to dissipative force, the mechanical energy of a wooden block sliding on a rough horizontal surface is not conserved.

Neglecting air resistance, an object moving vertically upward gains kinetic energy and loses an equal amount of gravitational potential energy

41.

A wheel rotating at angular speed of 20rev/s is brought to rest after 40 rev under a constant angular acceleration. The angular acceleration of a point on the wheel is

42.

The parallel axis theorem states that if I_cm is the moment of inertia of a body of mass M about an axis passing through its center of mass (cm), its moment of inertia about any axis

43.

Three forces of equal magnitude are exerted at the center of a uniform beam of length L and negligible mass, as shown in the Figure.

44.

Tensile stress is the

ratio of original to the change in length of the object.

parallel component of the applied force divided by the cross sectional area of an object.

perpendicular component of the applied force divided the cross sectional area of an object.

ratio of change in length of an object to the original length.

45.

A certain fluid has a density of 1080 kg/m³ and is observed to rise to a height of 2.1 cm in a 1.0 mm diameter tube. If the contact angle between the wall and the surface is zero, the surface tension of the fluid is

0.02835 N/m

5760 N/m

0.0567 N/m

0.1134 N/ m

46.

A slab of thermal insulator has a cross-section of 1 m 2 , a length 0 .2 cm, and thermal conductivity of 0. 1 J/(m.s°C). If the temperature difference between the opposite faces of the insulator is 100° C, the amount of heat flowing through the slab in 24 h is

4.32x10 J

5.0X10¹³

12 x 10³ J

7.2X10 J

47.

A 100 J of work is done on a system and 418.6 J of heat is extracted from it. According to the first law of then Mo dynamics, the change in the internal energy of the system is

518.6 J

-518. 6 J

318.6 J

-318.6 J

48.

Which of the following statements describe the difference between reversible and irreversible processes?

Ice at 0° C placed in a metallic can at 40° C undergoes a reversible process; whereas ice at 0° C placed in a metal can at 0° C undergoes an irreversible process.

A system undergoing reversible process is always close to thermodynamic equilibrium, whereas a system undergoing irreversible process is not in thermal equilibrium.

In an irreversible process, a system can move from one thermodynamic state to another and back to its initial state; whereas a system in a reversible process cannot move back to its initial state.

A process is reversible if its entropy increases, but irreversible if its entropy is constant.

49.

Which one of the following statements is correct about resonance in an oscillating object?

Dumping increases the amplitude and natural frequency of the oscillator.

At resonance, the driving frequency is equal to the natural in frequency and the amplitude becomes maximum,

Resonance occurs when the oscillator is subject to a constant driving force.

Resonance occurs when the frequency of a periodic driving force is greater than the natural frequency of the oscillator.

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