Physics 2009 | Study Mode

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Question 31
A
3.00 s
B
0.12 s
C
0.33 s
D
1.50 s
Explanation.
Half-life, T (1)/2 = (0.693)/ = (0.693)/ 0.231 = 3.0sec

Correct Option:
A
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Question 32
A
3.47 x 1018
B
6.93 x 10 20
C
3.47 x 1020
D
6.93 x 1018
Explanation.
The number of disintegration,N in time interval At, is given by
- N = Nt
Where N is the number of atoms present at the time t
But ^ = (0.693)/T
N = (0.693)/1(1)/2 Nt = (0.693 x 10)20 x 10/20 = 3.47 x 1018

Correct Option:
A
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Question 33
A
- rays are produced
B
holes are produced
C
x - rays are produced
D
electrons leave a hot element
Explanation.
Thermionic emission is ejection of electron from a metal surface as a result of heating.

Correct Option:
D
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Question 34
A
germanium
B
silicon
C
grapefruit
D
copper
Explanation.
Metals are good conductors due to the presence of free electrons

Correct Option:
D
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Question 35
A
a p-type semiconductor
B
an n-type semiconductor
C
an insulator
D
an intrinsic semi-conductor
Explanation.
When a pentavalent (5 outer electron)atom is added to a pure semiconductor, there is an extra electrons which does not take part in the covalent bonding resulting in an n-type semiconductor.

Correct Option:
B
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Question 36
A
2, -3, -2
B
-1, 3, -2
C
-1, 2, -3
D
-2, -1, 3
Explanation.
F M1M2
__r2


=> F = GM1M2
__r2

where F is the force of attraction
M1 and M2 are masses of the two bodies, r is the distance between them, and G is the universal gravitational constant
G = _Fr2
M1M2

dimension for force, F = ML = MLT-2
T.T

The dimension for G = MLT-2L2 = L3T-2
_MM_M

= M-1L3T-2
In comparison with MxLyTz, the values for x, y and z = -1, 3, -2

Correct Option:
B
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Question 37
A
117 kmh-1, N31oE
B
127 kmh-1, N31oE
C
117 kmh-1, N31oW
D
127 kmh-1, N31oW
Explanation.
R2 = 1002 + 602
10000 + 3600 = 13600
R = 13600 = 117km
60kml & = tan = 60/100
tan-1 0.6
= 31o west of the North
117km N31owPhy-explained-image

Correct Option:
C
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Question 38
A
100 m
B
50m
C
32 m
D
18 m
Explanation.
From S = ut + 1/2 at2
S = 1/2 ut2, since U = 0
Let S5 = distance in 5 seconds
= 1/2 x 4 x 52 = 2 x 25 = 50m
S4 = distance covered in 4 seconds
= 1/2 x 4 x 42 = 2 x 16 = 32m
Distance covered in the fifth second
S5 - S4 = 50m - 32m = 18m

Correct Option:
D
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Question 39
A
1.5 ms-1
B
1.4 ms-1
C
2.1 ms-1
D
1.7 ms-1
Explanation.
Sum of momentum before collision
M1 U1 + M2M2
12 x 4.2 + 18 x 0
12 x 4.2
= 50.4
Sum of momentum after collision
(m1 + m2)v
= (12 + 18)v
= 30v
V = 50.4/30
= 1.7ms-1

Correct Option:
D
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Question 40
A
upthrust is equal to the weight of the ball
B
ball accelerate uniformly
C
upthrustis equal to the velocity of the ball
D
velocity is uniform
Explanation.
At vt = terminal velocity
= zero acceleration
= uniform velocityPhy-explained-image

Correct Option:
D

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