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
B.
6 N
We know that, F = ma
Hence, from the figure
14 − N = 4a
14 − N = 8
N = 6 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 and x2 = A cos (ωt) ?
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