CBSE 11TH PHYSICS - Online Test

Answer : Option A
Explaination / Solution:

Let  ω$\omega$  be the angular velocity of the Ring of Mass M , thus the moment of inetia about given axis is  I1 =  MR2 and  the four point objects are genlty placed at perpendicular diameters at opposite end, so thus the distance of each object from axis of rotation is R, so  total moment of inetia of ring and four objects is  I2  = MR2+4mR2

According to law of conservation of angular momentum  I1 ω$\omega$ = I2ω$\omega$2 , So on solving ω2=(MR2MR2+4mR2)ω$)\omega$= MM+4m⋅ω

Answer : Option C
Explaination / Solution:

Addition of soap decreases the surface tension of water , as we know the energy of spraying is directly proportional to the surface tension .

Answer : Option C
Explaination / Solution:
No Explaination.

Answer : Option D
Explaination / Solution:

Base area of the boiler, A = 0.15 m2
Thickness of the boiler, l = 1.0 cm = 0.01 m
Boiling rate of water, R = 6.0 kg/min
Mass, m = 6 kg
Time, t = 1 min = 60 s
Thermal conductivity of brass, K = 109 J s –1 m–1 K–1
Heat of vaporisation, L = 2256 × 103 J kg–1
The amount of heat flowing into water through the brass base of the boiler is

Q=KA(T1−T2)lt     ..........(1)

where,
T1 = Temperature of the flame in contact with the boiler
T2 = Boiling point of water = 100°C 
Heat required for boiling the water

Q = mL  ....… (ii)
Equating equations (i) and (ii), we get:
∴ mL = KA(T1 - T2) t / l 
T1 - T2 = mLl / KAt
= 6 × 2256 × 103 × 0.01 / (109 × 0.15 × 60)
= 137.98 o C
Therefore, the temperature of the part of the flame in contact with the boiler is 237.98°C.

Answer : Option A
Explaination / Solution:

length, l = 4.234 m

breadth,b = 1.005 m

thickness, t = 2.01 cm = 2.01 × 10-2 m Area of the sheet = 2 (l × b + b × t + t × l) = 2 (4.234 × 1.005 + 1.005 × 0.0201 + 0.0201 × 4.234) = 2 (4.3604739) = 8.7209478 m​​​​​​2 

As area can contain a maximum of three significant digits, therefore, rounding off, we get Area = 8.72 m​​​​​​2

Answer : Option D
Explaination / Solution:
No Explaination.

Answer : Option D
Explaination / Solution:

Initial velocity u = 0 m/s

final velocity = v 

Time t = 2 s

Acceleration a = 1 m/s​​​​​​2

We know,

v = u + at

=>v=0+1×2

=> v = 2 m/s

Answer : Option B
Explaination / Solution:
No Explaination.

Answer : Option B
Explaination / Solution:

The motorcycle’s x- and  y-coordinates at t=0.50 s are

  x = vox t= 9.0×0.50 =4.5 m

y= −12gt2 = −12×9.8×(0.50)2 -1.2m

The negative value of y shows that the motorcycle is below its starting point.

The motorcycle’s distance from the origin at t=0.50 s is r= x2+y2−−−−−−√=(4.5)2+(−1.2)2−−−−−−−−−−−−−√=4.7 m

Answer : Option C
Explaination / Solution:
No Explaination.