Physics Test 198

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Physics Test 198

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Weekly Quiz Competition

Question 1
4 / -1

An electric lamp is connected to 220 V, 50 Hz supply. Then the peak value of voltage is

A
210 V

B
211 V

C
310 V

D
320 V

Solution

Solution :- V(0) = Vrms × 2

= 220 × √2

= 310
Question 2
4 / -1

In a step-up transformer the voltage in the primary is 220 V and the current is 5A. The secondary voltage is found to be 22000V. The current in the secondary (neglect losses) is

A
5 A

B
50 A

C
500 A

D
0.05 A

Solution
Question 3
4 / -1

A body moves along a circular path of radius 10 m and the coefficient of friction is 0.5. What should be the angular velocity of the body, if it is not to slip on the surface?

A
0.1 rad-s^-1

B
0.7 rad-s^-1

C
5 rad-s^-1

D
10 rad-s^-1

Solution
Question 4
4 / -1

K.E. of emitted cathode rays is dependent on

A
Only voltage

B
Only work function

C
Both (a) and (b)

D
It does not depend upon any physical quantity

Solution

Higher the voltage, higher is the KE. Higher the work function, smaller is the KE.
Question 5
4 / -1

A semi circle arc of radius 'a' is charged uniformly and the charge per unit length is λ. The electric field at its centre is

A
λ/2 π ∈₀ a²

B
λ/2 π ∈₀ a

C
λ²/2 π ∈₀ a

D
λ/4 ∈₀ a

Solution
Question 6
4 / -1

A gun fires the bullets each of mass 10 g with a velocity of 50 m−s^-1. If 1000 bullets are fired per second, then thrust on the shoulder will be

A
250 N

B
400 N

C
450 N

D
500 N

Solution

Mass of bullet

m=0.01Kg

v=50m/s

n=1000

Force on the man is equal to the change in momentum of the bullets coming out of the gun

F = mvn/t

F=(0.01×50×1000)/1

Therefore, F = 500N
Question 7
4 / -1

An electric dipole is placed along the X-axis at the origin O. A point P is at a distance of 20 cm from this origin such that OP makes an angle π/3 with the X axis. If electric field at P makes an angle θ with X-axis, the value of θ is

A
π/3

B
π/3 + tan^-1(√3/2)

C
3π/2

D
tan^-1√3/2

Solution
Question 8
4 / -1

A metre stick AB hinged (without friction) at the end A as shown in the figure is kept horizontal by means of a string tied to the end B, the other end of the string being tied to a hook. The string is carefully cut (or burnt), and the scale executes angular oscillations about an axis passing through the end A. What is the speed of the end B when the metre stick assumes vertical position immediately after the string is burnt? (Acceleration due to gravity = 10 ms^–2)

A
2.5 ms^–1

B
4.2 ms^–1

C
5.4 ms^–1

D
6.8 ms^–1

Solution

The centre of gravity of the metre stick is at its middle. When the string is burnt, the height of the centre of gravity is reduced by 0.5 m, thereby reducing the gravitational potential energy of the metre stick by Mgh= M×10×0.5 = 5M joule, where M is the mass of the metre stick.

The decrease in the potential energy is equal to the increase in kinetic energy. Therefore in the vertical position of the metre stick, its kinetic energy

(½)Iω² = 5M

Since the moment of inertia of a uniform bar of length L about a normal axis through ite mid point is ML²/12, its moment of inertia about a parallel axis through its end is ML²/3. [You will get this by applying the parallel axis theorem (see the post dated 2o^th January 2008)]

Therefore, we have (½)(ML²/3)ω² = 5M

Since ω = v/L and L = 1 metre, the above equation becomes

v²/6 = 5, from which v = √30 = 5.4 ms^–1 (approximately).
Question 9
4 / -1

Directions For Questions

The symbolic representation of four logic gates are given below:

...view full instructions

The logic symbols for OR, NOT and NAND gates are respectively:

A
(iv), (i), (iii)

B
(iv), (ii), (i)

C
(i), (iii), (iv)

D
(iii), (iv), (ii)

Solution
Question 10
4 / -1

In a capillary tube, water rises upto 3 mm. The height of water that will rise in another capillary tube having one-third radius of the first is

A
1 mm

B
3 mm

C
6 mm

D
9 mm

Solution

The narrower the tube, the higher is the rise in water.

When a glass capillary

h=2Tcosθ/Rpg

h∝1/R

h2/h1=R1/R2

3/h2=1/3

h2=9mm