An electric bulb marked as 50 W-200 V is connected across a 100 V supply. The present power of the bulb is

• 37.5 W

• 25 W

• 12.5 W

• 10 W

Three blocks of masses 4 kg, 2 kg, 1 kg respectively are in contact on a frictionless table as shown in the figure. If a force of 14 N is applied on the 4 kg block, the contact force between the 4 kg and the 2 kg block will be

• 2 N

• 6 N

• 8 N

• 14 N

In a mercury thermometer, the ice point (lower fixed point) is marked as 10° and the steam point (upper fixed point) is marked as 130°. At 40°C temperature, what will this thermometer read ?

• 78°

• 66°

• 62°

• 58°

Water is flowing through a very narrow tube. The velocity of water below which the flow remains a streamline flow is known as

• relative velocity

• terminal velocity

• critical velocity

• particle velocity

A train approaching a railway platform with a speed of 20 ms^-1 starts blowing the whistle. Speed of sound in air is 340 ms^-1. If the frequency of the emitted sound from the whistle is 640 Hz, the frequency of sound to a person standing on the platform will appear to be

• 600 Hz

• 640 Hz

• 680 Hz

• 720 Hz

What is the phase difference between two simple harmonic motions represented by ${\mathrm{x}}_1 = \mathrm{A} \sin \left(\mathrm{\omega t} + \frac{\mathrm{\pi }}{6}\right)$ and x₂ = A cos (ωt) ?

• $\frac{\mathrm{\pi }}{6}$

• $\frac{\mathrm{\pi }}{3}$

• $\frac{\mathrm{\pi }}{2}$

• $\frac{2\mathrm{\pi }}{3}$

17.

Heat is produced at a rate given by H in a resistor when it is connected across a supply of voltage V. If now the resistance of the resistor is doubled and the supply voltage is made V/3, then the rate of production of heat in the resistor will be

• H/18

• H/9

• 6H

• 18H

When a spring is stretched by 10 cm, the potential energy stored is E. When the spring is stretched by 10 cm more, the potential energy stored in the spring becomes

• 2 E

• 4 E

• 6 E

• 10 E

The frequency of the first overtone of a closed pipe of length l₁ is equal to that of the first overtone of an open pipe of length l₂. The ratio of their lengths (l₁ : l₂) is

• 2 : 3

• 4 : 5

• 3 : 5

• 3 : 4

A body when fully immersed in a liquid of specific gravity 1.2 weighs 44 gwt. The same body when fully immersed in water weighs 50 gwt. The mass of the body is

• 36 g

• 48 g

• 64 g

• 80 g