1
Ratio of voltages in a step up transformer is 8. If voltage at primary is 120 volt then the voltage at the secondary will be:
(1) 960 Volt (2) 180 Volt
(3) 120 Volt (4) 150 Volt
2 Motion of System of Particles and Rigid Body
A mass is whirled in a circular path with a constant angular velocity and its angular momentum is L. If the length of string is now halved keeping the angular velocity the same, the new angular momentum is:
1) L /4 2) L /2 3) L 4) 2L
Angular momentum, $$L= mvr$$
3 Ray Optics
A beam of monochromatic ligh first travels through glass of R.I. 1.5 and then through water (R.I. =4/3). If the difference in their wavelength in the two media is 40nm, then the wavelength of the monochromatic light in vacuum will be 1) 4000 Å 2) 4400 Å 3) 4800 Å 4) 5200 Å
$$\displaystyle{5200}Å$$ $$\displaystyle\therefore\lambda_{{w}}-\lambda_{{g}}=\lambda_{{a}}{\left[\frac{{{3}}}{{{4}}}-\frac{{{2}}}{{{3}}}\right]}=\frac{{\lambda_{{a}}}}{{{12}}}={40}\times{10}^{{-{9}}}$$
∴λa=12×40×10−9 = 4800Å
4 Oscillations
A pendulum is hung from the roof of a sufficiently high building and is moving freely to and fro like a simple harmonic oscillator. The acceleration of the bob of the pendulum 20 m/s2 at a distance of 5 m from the moving position. The time period of oscillation is?
1) 2s 2) 2πs 3) 1s 4) πs
Since in SHM, magnitude of acceleration is given as
a=ω2x
20=ω2×5
ω=2ω=2
Now, Time Period (T),
T=2π / ω
T=π s
5 Gravitation
In order to place a satellite of mass m in circular orbit at a distance r from the center of a planet of mass M the speed of the satellite needs to be
1) ÖGm/r 2) Ö2gr 3) ÖGM/r 4) GM=r
6 Kinetic Theory of gases
Which one of the following statements about expansion is correct? (1) Pyrex glass expands much less than ordinary glass under the same conditions. (2) Liquids do not expand when heated (3) Gases do not expand when heated (4) Water expands uniformly from 0 C upwards
7 Kinetic Theory of gases
7 moles of a tetra-atomic non-linear gas A at 10 atm and T K are mixed with 6 moles of another gas B at T/3K and 5atm in a closed, rigid vessel without energy transfer with surroundings. If final temperature of mixture was 5T/6K, then atomcity of gas B is (Assuming all modes of energy are active)
1) 1 2) 4 3) 2 4) 3
$$C_{v}$$ of gas $$A= \displaystyle \frac{3}{2}R+ \displaystyle \frac{3}{2}R+6R=9R$$ Let $$C_{v}$$ of gas $$B=X$$ Heat lost by gas $$A=7 \times 9R \times (T- \displaystyle \frac{5T}{6})$$ Heat gained by gas $$B=6X( \displaystyle \frac{5T}{6}- \displaystyle \frac{T}{3})$$ $$\Rightarrow 63R( \displaystyle \frac{T}{6})=6X( \displaystyle \frac{T}{2})=X= \displaystyle \frac{7}{2}R$$ $$\therefore$$ gas is diatomic. and atomcity of gas is 2.
8 Physical world and measurement
The pitch of a screw gauge is 1mm and there are 100 divisions on circular scale. When faces A and B are just touching each without putting anything between the studs 32nd division on the circular scale coincides with reference line. When a glass plate is placed between the studs, the linear scale reads 4 divisions and the circular scale reads 16 divisions. Find the thickness of the glass plate. Zero of linear scale is not hidden from circular scale when A and B touches each other.
1) 3.841mm 2) 3.84mm 3) 3.85mm 4) 3.846mm
As zero is not hidden from cricular scale when A and B touches each other.
Hence, the screw gauge has positive error. e=+n(LC)=32×0.01=0.32 mm Linear scale reading =4×(1mm)=4mm Circular scale reading =16×(0.01mm)=0.16mm ∴ Measured reading-e =(4+0.16)mm=4.16 mm ∴ Absolute reading = Measured reading-e =(4.16−0.32)mm=3.84mm Therefore, thickness of the glass plate is 3.84mm.
9 Ray Optics
An orange light ray and a green light ray pass from an acrylic block to air with the same angle of incidence of 45o . The orange is less deflected because:
(1) the index of refraction in acrylic for green light is greater than that of orange.
(2) the index of refraction in acrylic for green light is less than that of orange.
(3) the indices of refraction of both colors are greater in air than in acrylic.
(4). the indices of refraction of both colors are greater in acrylic than in air.
10 Laws of Motion
A 1,200-kilogram car traveling at 10. meters per second hits a tree and is brought to rest in 0.10 second. What is the magnitude of the average force acting on the car to bring it to rest? 1) 1.2 × 102N 2) 1.2 × 103N 3) 1.2 × 104N 4) 1.2 × 105N
Solution
F = m x a
F = 1200 x -100, ==> F = -120000 N (- sign indicted in the opposite direction)
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