Physics Test 270

Result

Physics Test 270

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Weekly Quiz Competition

Question 1
4 / -1

A circular steel wire 2.00 m long must stretch no more than 0.25 cm when a tensile force of 400 N is applied to each end of the wire. What minimum diameter is required for the wire? Young's modulus for steel: E = 20 × 10¹⁰ Pa.

A
1.4 mm

B
10 mm

C
1.5 mm

D
12.4 mm

Solution
Question 2
4 / -1

Water is flowing continuously from a tap having an internal diameter 8 × 10^-3m. The water velocity as it leaves the tap is 0.4 ms^-1. The diameter of the water stream at a distance 2 × 10^-1 m below the tap is close to

A
7.5 × 10^-3 m

B
9.6 × 10^-3 m

C
3.6 × 10^-3 m

D
5.0 × 10^-3 m

Solution
Question 3
4 / -1

A

B

C

D

Solution

The density of ball should be greater than liquid 1 because it sinks in it.

Also density of ball should be less than density of liquid 2 as it floats on it.
Question 4
4 / -1

There are two identical small holes on the opposite sides of a tank containing a liquid. The tank is open at the top. The difference in height between the two holes is h. As the liquid comes out of the two holes, the tank will experience a net horizontal force proportional to

A
√h

B
h

C
h^3/2

D
h²

Solution

Let ρ = density of the liquid.

Let α = area of a cross-section of each hole.

Volume of liquid discharged per second at a hole = αv.

Mass of liquid discharged per second = αvρ.

Momentum of liquid discharged per second = αv²ρ.

∴ the force exerted at the upper hole (to the right) = αρv2²

and the force exerted at the lower hole (to the left) = αρv1²

Net force on the tank = 2αρgh.
Question 5
4 / -1

Two soap bubbles with radii come in contact. Their common surface has a radius of curvature r. Then

A

B

C

D

Solution
Question 6
4 / -1

In an adiabatic process internal energy of gas

A
Increases

B
Become twice

C
Does not change

D
Decreases

Solution

From the first law of thermodynamics,

we know, dU = dQ - dW ; (work done BY the system is considered +ve)

For an adiabatic process, dQ = 0, and hence, dU = -dW

For an ideal gas expansion, we see that work done

BY the system is +ve (recall the sign convention for work done), i.e., dW > 0.

Therefore, dU is less than 0, and thus, the internal energy decreases.
Question 7
4 / -1

At what temperature is the r.m.s velocity of a hydrogen molecule equal to that of an oxygen molecule at 47°C?

A
80 K

B
–73 K

C
3 K

D
20 K.

Solution
Question 8
4 / -1

A
2/3

B
1/2

C
1

D
1/3

Solution
Question 9
4 / -1

Heat generated through a resistive wire will increase _______ times in unit time, if current in the wire becomes twice.

A
2

B
4

C
0.5

D
None of the above

Solution

So heat is given by

H = I² Rt

time is fixed, unit time, Resistance of wire will remain the same.

H ∝ I²

So,

H = k I² ---(1)

if the current becomes twice'

H' = k (2I)² ---(2)

So we see, the heat generated in unit time becomes 4 times of its initial value.
Question 10
4 / -1

A sphere of mass m and diameter D is Heated by temperature ΔT , if Coefficient of linear expansion is α what will be the change in the Surface Area

A
π D²α ΔT (α ΔT+ 2)

B
π D²α ΔT (α ΔT- 2)

C
π D²α ΔT (α ΔT+ 4)

D
π D²α ΔT (α Δ- 4)

Solution

Initial Surface Area = 4πR²

= 4 π (D/2)²

= 4 π D² / 4 = π D²

Surface Area at ΔT

= 4π(D^'/2)²

Now

D^'=D(1+α ΔT)

So Surface Area at ΔT

= 4π(D²/4 )(1+α ΔT)²

= π D² (1+ α²ΔT² + 2α ΔT)

Change in surface Area

= π D² (α²ΔT² + 2α ΔT)

= π D²α ΔT (α ΔT+ 2)