Physics Test 50

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Physics Test 50

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Weekly Quiz Competition

Question 1
4 / -1

A simple pendulum hanging from the ceiling of a stationary lift has a time period t₁. When the lift moves downwards with a constant velocity, the time period becomes t₂. Then

A
t₂is infinity

B
t₂ > t₁

C
t₂ < t₁

D
t₂ = t₁

Solution

The lift is moving with a constant velocity so, the acceleration will be zero. Thus, the time period will remain the same.

Hence, the correct option is (D).
Question 2
4 / -1

Electromagnetic waves of frequencies higher than 9√2 MHz are found to be not reflected by the ionosphere on a particular day at a place. The maximum electron density in the ionosphere is

A
√5 x 10²³ m ^-3

B
√2 x 10²³ m ^-3

C
2 x 10¹² m ^-3

D
5 x 10¹² m ^-3

Solution
Question 3
4 / -1

A satellite of mass m is placed at a distance r from the centre of Earth (mass M). The mechanical energy of the satellite is

A
- GMm/r

B
GMm/r

C
GMm/2r

D
- GMm / 2r

Solution
Question 4
4 / -1

A magnetising field of 1500Am⁻¹ produces flux of 2.4×10⁻⁵ weber in a iron bar of the cross-sectional area of 0.5 cm². The permeability of the iron bar is

A
245

B
250

C
252

D
255

Solution
Question 5
4 / -1

A boatman can row at a speed of 10kmh⁻¹. If a river of width 2 km flows at 5kmh⁻¹, then find the direction in which the boatman should row to reach a point on the other bank directly opposite to the point from where he started.

A
90^∘ to the direction of flow

B
60^∘ towards NW

C
120^∘ to the direction of flow

D
Along the flow

Solution

To reach a point directly opposite, horizontal velocity should be zero. Let boatman's velocity in still water be = ′b′ .

Let river's flow rate be "r".

Then,
Question 6
4 / -1

A stone released with zero velocity from the top of a tower reaches the ground in 4 s. The height of the tower is (g = 10 m/s²)

A
20 m

B
40 m

C
80 m

D
160 m

Solution
Question 7
4 / -1

A container of volume 1 m³ is divided into two equal parts by a partition. One part has an ideal gas at 300 K and the other part contains a vacuum. The whole system is thermally isolated from the surroundings.

When the partition is removed, the gas expands to occupy the whole volume. Its temperature will now be

A
Halved

B
Doubled

C
The same

D
None of these

Solution

Since the system is insulated, the before dQ = 0.

In part, there is no pressure (because of the Vacuum)

So, work done dW = PdV = 0

From dQ = dU + dW, we get dU=0

Since, U depends on temperature, so dU = 0

This means that there is no change in temperature.

Hence, the correct option is (C).
Question 8
4 / -1

Compute the fractional change in volume of a glass slab, when subjected to a hydraulic pressure of 10 atm. Bulk modulus of glass 37 GPA.

A
0.0022

B
0.0027

C
0.0024

D
0.0030

Solution
Question 9
4 / -1

An asteroid of mass m is approaching earth, initially at a distance 10R_e with speed v_i. It hits earth with a speed v_f(R_e and M_e are radius and mass of the earth), then

A

B

C

D

Solution

Applying law of conservation of energy for asteroid at a distance 10R_e and at earth's surface,
Question 10
4 / -1

Pure silicon at 300 K has equal electron (n_e) and hole (n_h) concentration of 1.5 × 10¹⁶m⁻³. Doping by indium increases n_h to 4.5 ×10²²m⁻³. The n_e in the doped silicon is:

A
3 × 10⁹m^-3

B
4 × 10⁹m^-3

C
5 × 10⁹m^-3

D
6 × 10⁹m^-3

Solution