cbse 11th physics | Online Objective Test

Thermodynamics Prepare / Learn

Q1. In changing the state of a gas adiabatically from an equilibrium state A to another equilibrium state B, an amount of work equal to 22.3 J is done on the system. If the gas is taken from state A to B via a process in which the net heat absorbed by the system is 9.35 cal, how much is the net work done by the system in the latter case?

A. 17.2 J

B. 17.6 J

C. 16.8 J

D. 17.9 J

Answer : Option C
Explaination / Solution:

$Δ Q = Δ U + W$

In adiabatic process $Δ Q = 0$

$Δ U = - W$

Given that W = -22.3J

$Δ U = 22.3 J$

in second process $Δ Q = 9.35 \times 4.18 = 39.083 J$

$Δ Q = Δ U + W$

$\begin{aligned} Δ Q = 9.35 \times 4.18 = 39.083 J \\ Δ Q = Δ U + W \\ 39.083 = 22.3 + W \\ W = 16.8 J \end{aligned}$

Laws of Motion Prepare / Learn

Q2. A body of mass 5 kg is acted upon by two perpendicular forces 8 N and 6 N. Give the magnitude and direction of the net force acting on the body.

A. 14 N at an angle of 37

^{\circ}

to the 8 N force

B. 16 N at an angle of 46

^{\circ}

to the 8 N force

C. 12 N at an angle of 36

^{\circ}

^{\circ}

towards the 8 N force

D. 12 N at an angle of 38

^{\circ}

to the 8 N force

Answer : Option C
Explaination / Solution:

Let F1 = 8N & F2 = 6 N.

then the resultant force is $F = \sqrt{F_{1}^{2} + F_{2}^{2}}$

= $\sqrt{8^{2} + 6^{2}}$

= 10N

The direction is determined as $t a n θ = \frac{F_{2}}{F_{1}}$

= 6/8

therefore $θ = 36^{o} 52^{o}$

Work Energy and Power Prepare / Learn

Q3. A railway porter is holding a weight of 100 kgs on his head and is standing still. What is the work done by him?

A. 0 J

B. 100 J

C. 200 J

D. 1000 J

Answer : Option A
Explaination / Solution:

W = Force x displacement in the direction of force Work done will be zero because porter is stationary (i.e. displacement is zero)

Physical World Prepare / Learn

Q4. One example where technology predates science is

A. laser surgery

B. Radio

C. Steam engine

D. TV

Answer : Option C
Explaination / Solution:

Thomas Newcomen's atmospheric engine was the first commercial true steam engine using a piston, and was used in 1712 for pumping in a mine. They became popular for mining and 104 were in use by 1733, eventually over two thousand of them were installed. In1781 Scottish engineer James Watt patented a steam engine that produced continuous rotary motion. Watt's ten-horsepower engines enabled a wide range of manufacturing machinery to be powered. The engines could be sited anywhere that water and coal or wood fuel could be obtained.

System of Particles and Rotational Motion Prepare / Learn

Q5. A uniform rod of mass 2 kg is 1 meter long. Its radius of gyration about an axis through its one end and perpendicular to its length in SI units is

A. 2 /

\sqrt

(3)

C. 1 /

\sqrt

(3)

D. 1/ 2

\sqrt

(3)

Answer : Option C
Explaination / Solution:

Moment of inertia of rod about an axis through its one end and perpendicular to its length

$I = M L 2 3$ M = 2 KgL = 1 mMoment of inertia of rod in terms of radius of gyrationI = Mk2 $M L 2 3 = M k 2 k = L 2 3 - - - \sqrt = L 3 - \sqrt = 1 3 - \sqrt$

Mechanical Properties of Fluids Prepare / Learn

Q6. Two small drops of mercury, each of radius r, form a single large drop. The ratio of surface energy before and after this change is

A. 1:2

^{1 / 3}

B. 1:2

C. 2

^{1 / 3}

D. 2:1

Answer : Option A
Explaination / Solution:

Kinetic Theory Prepare / Learn

Q7.

At what temperature is the root mean square speed of an atom in an argon gas cylinder equal to the rms speed of a helium gas atom at – 20 $^{\circ} C$ ? (Atomic mass of Ar = 39.9 u, of He = 4.0 u).

A. 2.26

\times

1 0^{3}

B. 2.77

\times

1 0^{3}

C. 2.52

\times

1 0^{3}

D. 2.63

\times

1 0^{3}

Answer : Option C
Explaination / Solution:

vAr=vHe3RT39.9−−−−−√=3R×2534−−−−−−−−√T=39.9×2534=2.52×103K

Thermal Properties of Matter Prepare / Learn

Q8. Which of the following statement(s) is/are true? (I) Every substance contains heat. (II) For heat to flow between two substances, they must be at different temperatures. (III) The internal energy of a substance is equal to the kinetic energy of the molecules in the substance.

A. I and II only

B. II only

C. II and III only

D. III only

Answer : Option B
Explaination / Solution:

Heat is the form of energy that is transferred from one body to another as the result of a difference in temperature

Units and Measurements Prepare / Learn

Q9.

How many g $c m^{2} s^{- 2}$ does 1 kg $m^{2} s^{- 2}$ equal?

A. 107

B. 103

C. 105

D. 108

Answer : Option A
Explaination / Solution:

We know 1 kg = 103 g

1 m2 = 104 cm

1 s-2 = 1s-2

multiply all these quantities we get

=> 1 kg m2 s-2 = $10^{3} \times 10^{4} g c m^{2} s^{- 2}$

$=> 1 k g m^{2} s^{- 2} = 10^{7} g c m^{2} s^{- 2}$

Oscillations Prepare / Learn

Q10. The period of a spring oscillating simple harmonically is

A. T=2

π \sqrt{{\frac{m}{K}}}

B. T=2

π

\sqrt{{\frac{K}{m}}}

C. T=2

π \sqrt{{\frac{m}{2 K}}}

D. T=2

π \sqrt{{\frac{m}{2 K}}}

Answer : Option D
Explaination / Solution:
No Explaination.

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