Physics Test

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Physics Test - 20

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Question 1
1 / -0

A body floats in a liquid contained in a beaker. The whole system falls freely under gravity. The upthrust on the body due to the liquid is

A
zero

B
equal to the weight of the liquid displaced

C
equal to the weight of the body in air

D
equal to the weight of the immersed portion of the body

Solution

For a body falling freely under gravity, the effective value of g is zero. Hence, the upthrust is zero.
Question 2
1 / -0

A small drop of water of surface tension is squeezed between two clean glass plates, so that a thin layer of thickness d and area A is formed between them. If the angle of contact is zero, then the force required to pull the plates apart is

A

B

C

D

Solution
Question 3
1 / -0

A body of density ρ is dropped from rest at a height 'h' into a lake of density 'σ', where σ > ρ . Neglecting all the dissipative forces, calculate the maximum depth to which the body sinks before returning to float on the surface.

A

B

C

D

Solution
Question 4
1 / -0

A small particle is released inside the depth of a liquid in the vessel. The volume of the particle is V. Density and viscosity of the liquid are ρ and η, respectively. Buoyant force on the particle is greater than the weight of the particle. The variation of velocity of the particle with time is

A

B

C

D

Solution

Initially the up thrust is more than its weight, so it will accelerate, i.e. its velocity increases. As the viscosity increases, the viscous force also increases. The acceleration decreases at a time when the viscous force and the weight acting downward balance the up thrust. Finally, the acceleration will become zero and it will move with a constant velocity.
Question 5
1 / -0

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
Question 6
1 / -0

The Leaning Tower of Pisa does not fall because

A
it is tapered at the top.

B
it covers a large base area.

C
the vertical line passing through the centre of gravity of the tower falls within its base.

D
its centre of gravity remains at the lowest position.

Solution

The Leaning Tower of Pisa does not fall because the vertical line through the centre of gravity of the tower falls within its base.
Question 7
1 / -0

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

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 8
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If Earth suddenly contracts to 1.5% of its present size, without any change in its mass, then how would the value of acceleration due to gravity change?

A
2%

B
3%

C
4%

D
5%

Solution
Question 9
1 / -0

Kepler's second law states that the straight line joining a planet to the sun sweeps out equal areas in equal time. This statement is equivalent to the statement that

A
total acceleration is zero

B
tangential acceleration is zero

C
longitudinal acceleration is zero

D
radial acceleration is zero

Solution

Earth and all other planets move around the sun under the effect of gravitational force. This force always acts along the line joining the centre of the planet and the sun and is directed towards the sun. In other words, a planet moves around the sun under the effect of a purely radial force. Therefore, areal velocity of the planet must always remain constant.
Question 10
1 / -0

The angular velocity of a planet revolving in an elliptical orbit around the sun __________ when it comes near the sun

A
decreases

B
increases

C
remains the same

D
None of these

Solution