Physics Test

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Physics Test - 3

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Question 1
4 / -1

The excess pressure inside a spherical drop of water is four times that of another drop. Then, their mass ratio is

A
1 : 16

B
8 : 1

C
1 : 4

D
1 : 64

Solution

Explanation:
Question 2
4 / -1

A hollow metallic sphere, filled with water, is hung from a support by a long thread. A small hole is made at the bottom of the sphere and it is oscillated. How will the time period of oscillations be affected as water slowly flows out of the hole?

A
The time period will remain unchanged as water is flowing out.

B
The time period will keep increasing until the sphere is empty.

C
The time period will keep decreasing until the sphere is empty.

D
The time period will increase at first then decrease untill the sphere is empty; finally the period will be the same as that when the sphere was full of water.

Solution

Explanation:

The length of the pendulum (I) is the distance between the point of support and the centre of mass of the sphere. The centre of mass (CM) of a sphere is at its centre when it is empty and completely filled with water. The CM falls below the centre of the sphere as the water flows out until the mass of the water becomes same as the mass of the sphere after which CM will shift upward and the CM will return to its original value . Hence, the effective length of the pendulum (and hence, its time period) will increase then decreases and when sphere is empty then it becomes equal to the time period when the sphere was full of water. Thus, the correct choice is (4).
Question 3
4 / -1

Match the following:

A
A - 4, B - 3, C - 1, D - 2

B
A - 1, B - 4, C - 2, D - 3

C
A - 3, B - 1, C - 4, D - 2

D
A - 2, B - 4, C - 1, D - 3

Solution

Explanation:

Unit of magnetic field intensity is Am^-1.

Unit of magnetic flux is Wb (weber)

Unit of magnetic potential is Wbm^-1.

Unit of magnetic induction is Wnm^-2.
Question 4
4 / -1

A body of mass 1 kg is projected with velocity 40 m/s at an angle of projection 30° with the horizontal. The magnitude of change in momentum from t = 0 to t = 2 sec is

A
20 Ns

B
30 Ns

C
10 Ns

D
10√3 Ns

Solution

Explanation:

In projectile motion, the horizontal component of the velocity of the projectile does not change; the vertical component of the velocity changes.

So, the change in momentum is due to change in the velocity of the projectile in vertical direction only.
Question 5
4 / -1

A body is dropped from height 'h'. If the coefficient of restitution is 'e', calculate the height achieved (h1) after one bounce.

A
h₁ = e²h

B
h₁ = e⁴h

C
h₁= eh

D
h₁ = h/e

Solution

Explanation:

If a body falls from a height 'h' onto a hard floor and rebounds to height h₁the coefficient of the restitution is defined as the ratio of the velocity of approach to the velocity of separation.

Velocity of approach
Question 6
4 / -1

If the values of each of length, mass and time are doubled, then the work done becomes

A
4 times

B
6 times

C
8 times

D
2 times

Solution

Explanation:
Question 7
4 / -1

A cord is wound around the circumference of a bicycle wheel (without tyre) of diameter 1 m. A mass of 2 kg is tied to the end of the cord and it is allowed to fall from rest. The weight falls 2 m in 4 s. The axle of the wheel is horizontal and the wheel rotates with its plane vertical. The angular acceleration produced is (Take g = 10 ms^–2)

A
0.5 rad s^–2

B
1.0 rad s^–2

C
2.0 rad s^–2

D
4.0 rad s^–2

Solution

Explanation:

We first find the linear acceleration a by using the relation
or

Hence the correct choice is (1).
Question 8
4 / -1

A thin uniform metallic triangular sheet of mass M has sides AB = BC = L as shown in the figure. What is its moment of inertia about axis AC lying in the plane of the sheet?

A
ML²/12

B
ML²/6

C
ML²/3

D
2ML²/3

Solution

Explanation:

It is clear from the figure that the moment of inertia of triangular sheet moment of inertia of a square sheet ABCD about its diagonal
Question 9
4 / -1

If the Earth stops rotating, the value of g at the equator will

A
increase

B
decrease

C
remain constant

D
Cannot be predicted

Solution

Explanation:

At the equator, the value of acceleration due to gravity is g' = g - ω²R.

If the Earth stops rotating, ω = 0, g' = g

So, the value of acceleration due to gravity will increase.
Question 10
4 / -1

A bird flies for 4 s with a velocity of |t - 2| m/s in a straight line, where t = time in seconds. It covers a distance of

A
2 m

B
4 m

C
6 m

D
8 m

Solution

Explanation:

Plot its velocity v against time t. The area under the curve gives the distance.

Area under the vt graph is