Physics Test 195

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Physics Test 195

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Question 1
4 / -1

A monoatomic gas is taken from A to C as shown in the figure. The temperature of gas at B is 27°C, then the change in internal energy of the gas is

A
15 J

B
20 J

C
30 J

D
25 J

Solution
Question 2
4 / -1

A rope hangs from a rigid support. A pulse is set by jiggling the bottom end. We want to design a rope in which velocity v of pulse is independent of z, the distance of the pulse from fixed end of the rope. If the rope is very long the desired function for mass per unit length µ(z) in terms of µ₀ (mass per unit length of the rope at the top (z = 0), g, v and z is :

A

B

C

D

Solution
Question 3
4 / -1

In the Pressure versus Volume graph shown, in the process of going from a to b 60 J of heat is added, and in the process of going from b to d 20 J of heat is added. In the process of going from a to c to d, what is the total heat added?

A
80 J

B
65 J

C
60 J

D
56 J

Solution

Q_abd – Q_acd
= (W_abd – W_acd) + (DU_abd – DU_acd)
= W_abd – W_acd + 0
(internal energy change is same for two paths)
= area of abdca = 15 J
Q_abd = Q_ab + Q_bd = 60 + 20 = 80 J Q_acd = Q_abd –15= 65 J

Alternative :
From the First law of Thermodynamics, one has
ΔU_a→c→d = Q_a→c→d + W_a→c→d = (60 J + 20 J) + [-(8Pa) (3m³)] ⇒ 56 J.
Since energy is a state variable, ΔU_a→c→d = Q_a→c→d + W_a→c→d⇒ 56 J
= Q + [-(3Pa) (3m³)] ⇒ Q_a→c→d = 65 J
Question 4
4 / -1

A glass tube of 1.0 meter length is filled with water. The water can be drained out slowly at the bottom of the tube. If a vibrating tuning fork of frequency 500Hz is brought at the upper end of the tube and the velocity of sound is 330m/s then the total number of resonances obtained will be

A
4

B
3

C
2

D
1

Solution
Question 5
4 / -1

A body of mass 25 kg is dragged on a rough horizontal floor for one hour with a speed of 2km/h.The coefficient of friction between the body and the surface in contact is 0.5 and half the heat produced is absorbed by the body. If specific heat of body is 0.1 cal g^–1 (⁰C)^–1, then the rise in temperature of body is

A
50 K

B
23.8 K

C
100 K

D
11.9 K

Solution

Friction force = 0.5 × 25 × 10 = 125 N distance moved = 2 × 10³

∴ work done against friction = 250 × 10³ J

∴ Heat given to the body = 125 × 10³ J
Question 6
4 / -1

There is a rectangular metal plate in which two cavities in shape of rectangle and circle are made, as shown in figure, with dimensions. P & Q are centres of these cavities. On heating the plate which of the following quantities increases.

A
πr²

B
ab

C
R

D
A, B, C are all correct

Solution

All dimension will increase
Question 7
4 / -1

A block of wood is floating in water at 0°C. The temperature of only water is slowly raised from 0°C to 10°C. With the rise in temperature of the water the volume of block above water level will be

A
increase

B
decrease

C
first increase and then decrease

D
first decrease and then increase

Solution

To keep Buoyent force constant volume of submerged part must increase.
Question 8
4 / -1

A rectangular block of lead has dimensions 4 cm × 3 cm × 20 cm. A temperature difference of 100°C can be applied to any pair of opposite faces that we choose.

A
The largest amount of heat flows if it flows parallel to line BG..

B
The largest amount of heat flows if it flows parallel to line AD.

C
The smallest amount of heat flows if it flows parallel to AF.

D
The smallest amount of heat flows if it flows parallel to AB.

Solution
Question 9
4 / -1

Two identical solid spheres have the same constant temperature. One of the spheres is cut into two identical pieces. These two hemispheres are then separated. The intact sphere radiates an energy Q during a given time interval at temperature T₀. During the same interval, the two hemisphere radiate at total energy Q' at temperature T₀. Emissivity of all the surfaces is same. The ratio Q'/Q has value :

A
0.50

B
0.75

C
2.0

D
1.5

Solution
Question 10
4 / -1

A car blowing a horn of frequency 350 Hz is moving normally towards a wall with a speed of 5 m/s. The beat frequency heard by a person standing between the car and the wall is (speed of sound in air = 350 m/s)

A
zero

B
3.5 Hz

C
5 Hz

D
10 Hz

Solution

Frequency observed by man is same as “observed” by wall and it reflects the same and as man and wall are relatively at rest, hence man observers same frequency of reflected sound. Hence no beat frequency