WBJEE 2013 online practice set 2

WBJEE 2013 LAST MINUTES SUGGESTION and PRACTICE SET 2 SUBJECT:PHYSICS

1. A Stone tied to a string of length L is whirled in a vertical circle, with the other end of the string at the center. AT a certain instant of time, the stone is at its lowest position and has a speed u. The magnitude of the change in its velocity as it reaches a position where the string is horizontal is a)√(2gL) b) √(u2-2gL) c)√(2(u2-gL)) d)√(u2-gL) Answer is : c) √(2(u2-gL))

2.A coin is placed on a horizontal platform, which undergoes vertical simple harmonic motion of angular frequency ω. The amplitude of oscilation is gradually increased. The coin will leave contact with the platform for the first time a)at the highest position of the platform b)at the mean position of the platform c)for an amplitude of g/ω2 d)a and c Answer is : d) a and c

3. Let ω be the angular velocity of the earth rotation about its axis. Assume that the acceleration due to gravity on the earth's surface has the same value at the equator and the pole. An object weighed by a spring balance gives the same reading at the euator as at a height h above the poles (h<<R). THe value of h is a)ω2R2/2g b)ω2R2/g c)2ω2R2/g d)√(Rg)/ω Answer is : a) ω2R2/2g

4. A satellite close to the earth is in orbit above the equator with a period of rotation of 1.5 hours. If it is above a point P on the equator at some time, it will be above P again after time a)1.5 hours b)1.6 hours if it is rotating from west to east c)24/17 hours if it is rotating from east to west d)b and c Answer is : d) b and c

5. For a satellite to be geostationary, which of the following are essential condition(s)? a)It must always be stationed above the equator b)It must rotate from west to east c)It must be above about 36000 km above the earth d)all of the above Answer is : d) all of the above

6. A rectangular block of mass m and area of cross-section A floats in a liquid of density ρ. If it is given a small vertical displacement from equilibrium, it undergoes oscillation with a time period T. a)T ∞√m b)T ∞1/√A c)T ∞1/√ρ d)All of the above Answer is :d) All of the above

7. A point starts from rest and moves along a circular path with a constant tangential acceleration. After one rotation, the ratio of its radial acceleration to its tangential acceleration will be equal to a)2π b)3π c)4 π d)1 Answer is : c) 4π

8. A uniform rod of mass m is hinged at its upper end. It is released from a horizontal position. When it reaches the vertical position, what force does it exert on the hinge a)2.5mg b)1.5mg c)2mg d)3.5mg Answer is : a) 2.5mg

9. A ring of mass m rolls down an inclined plane with a acceleration a without slipping. The plane makes an angel θ with the horizontal. The force of friction acting on the ring is equal to a)mg sinθ b)mg cosθ c)m(g sinθ-a) d)ma Answer is : d) ma

10. A simple pendulum has time period T. A uniform rod, whose length is the same as that of the pendulum, undergoes small oscillations about its upper end. Its time period of oscillation will be a) <T b)T c)>T d)may be a,b or c depending on whether T is <, = or > 2 seconds Answer is : a) <T

11. A system is taken from state A to state B along two different paths 1 and 2. The heat absorbed and work done by the system along these two paths are Q1 and Q2 and W1 and W2 respectively. a)W1=W2 b)Q1=Q2 c)Q1 + W1=Q2 + W2 d)Q1 - W1=Q2 - W2 Answer is : d) Q1 - W1=Q2 - W2

12. When an ideal diatomic gas heated at constant pressure, the fraction of the heat energy supplied which increases the internal energy of the gas is a)2/5 b)3/5 c)3/7 d)5/7 Answer is : d) 5/7

13. A body cools from 50°C to 40°C in 5 minutes. The surronding temperature is 20°C. In what further time (in minutes) will it cool to 30°C a)5 b)15/2 c)10 d)25/3 Answer is : d) 25/3

14. The first law of thermodynamics incorporates the concepts of a)conservation of energy b)equivalence of heat and work c)conservation of work d)a and b Answer is : d) a and b

15. For an Ideal gas a)the change in internal energy in a constant pressure process from temperature T1 to T 2 is equal to nCv(T2-T1), where Cv is the molar heat capacity at constant volume and n is the number of moles of the gas. b)the change in internal energy of the gas and work done by the gas are equal in magnitude in an adiabatic process. c)the internal energy does not change in an isothermal process. d)All of the above Answer is : d) All of the above

16. A planet is an average distance d from the sun, and its average surface temperature is T. Assume that the planet receives energy only from the sun and loses energy only through radiation from its surface. Neglect atmospheric effect. If T ∞d-n, the value of n is a)1 b)2 c)¼ d) ½ Answer is : d) ½

17. A string K has double the length, double the tension, double the diameter and double the densitya as another string R. Their fundamental frequencies of vibration are nK and nR respectively. The ratio nK/nR is equal to a)¼ b)½ c)¾ d)⅓ Answer is : a) ¼

18.Two identical sounds A and B reach a point in the same phase. The resultant sounds is C. The loudness of C is n dB higher then the loudness of A. The value of n is a)2 b)3 c)4 d)6 Answer is : d) 6

19. A A pipe of length 1 m is closed at one end. The velocity of sound in air is 300 m/s. The air column in the pipe will not resonate for sound of frequency a)375 Hz2 b)225 Hz c)300 Hz d)175 Hz Answer is : c) 300 Hz

20. If two waves of the form y=asin(ωt-kx) and y=acos(kx-ωt) are superposed, the resultant wave will have amplitude a)0 b)a c)2a d)√2g Answer is : d) √2g

Referance Books: Physics mcq - D Mukherjee, A guide to physics problem-- C.R.D.G

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