A bullet moving with a speed of 100 ms-1 can just penetrate two planks of equal thickness. Then, the number of such planks penetrated by the same bullet when the speed is doubled will be
6
10
4
8
D.
8
Let the thickness of each plank is d. From equation of motion
v2 = u2 + 2as ...... (i)
1st case : s = 2d , u = 100 ms-1 , v = 0
(− ve sign stands for retardation)
IInd case : Let the bullet with double the previous speed will penetrate n planks of equal thickness d.
Now, v = 0, u = 200 ms-1,
Using equation (1) again, we have
Two bodies of masses 1 kg and 2 kg have equal momentum. Then, the ratio of their kinetic energies is
2 : 1
3 : 1
1 : 3
1 : 1
The physical quantity having the same dimensions as Planck's constant h is
linear momentum
angular momentum
Boltzmann constant
force
A balloon is rising vertically up with a velocity of 29 ms-1 .A stone is dropped from it and it reaches the ground in 10 seconds. The height of the balloon when the stone was dropped from it is (g = 9.8ms-1)
400 m
150 m
100 m
200 m
Two equal forces (P each) act at a point inclined to each other at an angle of120°. The magnitude of their resultant is
P/2
P/4
P
2P
When a body moves in a circular path, no work is done by the force since
force and displacement are perpendicular to each other
the force is always away from the centre
there is no displacement
there is no net force
The difference between the apparent frequency of a source of sound as perceived by the observer during its approach and recession is 2% of the frequency of the source. If the speed of sound in air is 300 ms-1, the velocity of the source is
1.5 ms-1
12 ms-1
6 ms-1
3 ms-1
Curie-Weiss law is obeyed by iron
at Curie temperature only
at all temperatures
below Curie temperature
above Curie temperature