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Physics M.C.Q (1 Marks)

Model Paper 10 · Rajasthan Board (RBSE) STD 11 Science (Rajasthan - English Medium). 12 questions.

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M.C.Q (1 Marks)

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12 questions · timed · auto-graded

MCQ 11 Mark
As observed from earth, the sun appears to move in an approximate circular orbit. For the motion of another planet like mercury as observed from earth, this would
  • A
    not be true because the major gravitational force on mercury is due to sun
  • B
    not be true because mercury is influenced by forces other than gravitational forces
  • C
    be similarly true
  • D
    not be true because the force between earth and mercury is not inverse square law
Answer
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MCQ 21 Mark
The motor of an engine is rotating about its axis with an angular velocity of $100 rev / m$. It comes to rest in 15 s , after being switched off. Assuming constant angular deceleration, what are the number of revolutions made by it before coming to rest?
  • A
    40
  • B
    15.6
  • C
    12.5
  • D
    32.6
Answer
(c) 12.5
Explanation: Given
Time $= t =15 s=\frac{15}{60}=\frac{1}{4} min$
Angular displacement:
$
\theta=\left[\frac{\omega+\omega_0}{2}\right] t=\left[\frac{0+100}{2} \times \frac{1}{4}\right]=\frac{50}{4}=12.5 \text { revolutions }
$
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MCQ 31 Mark
Consider two rods of same length and different specific heats $\left( c _1, c _2\right)$, thermal conductivities $\left( K _1, K_2\right)$ and area of cross-sections $\left(A_1, A_2\right)$ and both having temperatures $\left(T_1, T_2\right)$ at their ends. If their rate of loss of heat due to conduction is equal, then:
  • A
    $\frac{K_2 A_1}{c_2}=\frac{K_1 A_2}{c_1}$
  • B
    $K _1 A_1= K _2 A_2$
  • C
    $K _2 A_1= K _1 A_2$
  • D
    $\frac{K_1 A_1}{c_1}=\frac{K_2 A_2}{c_2}$
Answer
(b) $K_1 A_1=K_2 A_2$
Explanation: Given: $\frac{Q_1}{t}=\frac{Q_2}{t}$
or $\frac{K_1 A_1\left(T_1-T_2\right)}{l}=\frac{K_2 A_2\left(T_1-T_2\right)}{l}$
or $K _1 A_1= K _2 A_2$
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MCQ 41 Mark
A Merry-go-round, made of a ring-like platform of radius $R$ and mass $M$, is revolving with angular speed $\omega$. A person of mass M is standing on it. At one instant, the person jumps off the round, radially away from the centre of the round (as seen from the round). The speed of the round afterwards is
  • A
    $2 \omega$
  • B
    $0$
  • C
    $\frac{\omega}{2}$
  • D
    $\omega$
Answer
(d) $\omega$
Explanation: As no torque is exerted by the person jumping, radially away from the centre of the round (as seen from the round), let the total moment of inertia of the system is 21 (round + Person (because the total mass
is 2 M ) and the round is revolving with angular speed wsince the angular momentum of the person when it jumps off the round is $1 \omega$ the actual momentum of round seen from ground is $2|\omega-|\omega=| \omega$
So we conclude that the angular speed remains same, i.e $\omega$
Image
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MCQ 61 Mark
The number of possible natural oscillations of air column in a pipe closed at one end of length 85 cm whose frequencies lie below 1250 Hz are (velocity of sound $=340 ms^{-1}$ )
  • A
    4
  • B
    6
  • C
    7
  • D
    5
Answer
(b) 6
Explanation: Fundamental frequency is $\nu=\frac{v}{4 l}=\frac{340 ms^{-1}}{4 \times 0.85 m}=100 Hz$
Only odd harmonics are present in the pipe closed at one end. So the possible harmonics less than 12500 Hz are 100 Hz, 300 Hz, 500 Hz, 700 Hz, 900 Hz, 1100 Hz
These are six in number.
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MCQ 91 Mark
A satellite is moving with a constant speed v in a circular orbit about the earth. An object of mass m is ejected from the satellite such that it just escapes from the gravitational pull of the earth. At the time of its ejection, the kinetic energy of the object is:
  • A
    $\frac{1}{3} m v^2$
  • B
    $mv ^2$
  • C
    $\frac{1}{2} m v^2$
  • D
    $\frac{2}{3} m v^2$
Answer
(b) $mv ^2$
Explanation: Escape speed $=\sqrt{2} \times$ orbital speed
$
v_e=\sqrt{2} v
$
At the time of its ejection, kinetic energy of the object will be
$
K=\frac{1}{2} m v_e^2=\frac{1}{2} m(\sqrt{2} v)^2=mv^2
$
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MCQ 101 Mark
A liquid is kept in a cylindrical jar, which is rotated about the cylindrical axis. The liquid rises at its ends. The radius of the jar is $r$ and speed of rotation is $\omega$. The difference in height at the centre and the sides of jar is
  • A
    $\frac{g}{r^2 g^2}$
  • B
    $\frac{r^2 \omega^2}{g}$
  • C
    $\frac{2 g}{r^2 \omega^2}$
  • D
    $\frac{r^2 \omega^2}{2 g}$
Answer
(d) $\frac{r^2 \omega^2}{2 g}$
Explanation: $m g h=\frac{1}{2} I \omega^2=\frac{1}{2} \times m r^2 \omega^2$
$
\therefore h=\frac{r^2 \omega^2}{2 g}
$
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MCQ 121 Mark
The equation of a wave travelling on a string is $y=4 \sin \left[\frac{\pi}{2}\left(8 t-\frac{x}{8}\right)\right]$ where $x , y$ are in cm and t in second. The velocity of the wave is
  • A
    $64 cms ^{-1}$, in -x direction
  • B
    $32 cm s ^{-1}$, in + x direction
  • C
    $32 cm s ^{-1}$, in -x direction
  • D
    $64 cms ^{-1}$, in + x direction
Answer
(d) $64 cms ^{-1}$, in + x direction
$
\begin{aligned}
& \text { Explanation: } y=4 \sin \left(4 \pi t-\frac{\pi}{16} x\right) \\
& \Rightarrow \omega=4 \pi, k=\frac{\pi}{6} \\
& v=\frac{\omega}{k} 64 cms^{-1} \text { along }+x \text { direction }
\end{aligned}
$
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M.C.Q (1 Marks) - Physics STD 11 Science Questions - Vidyadip