Physics Test 212

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Physics Test 212

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Weekly Quiz Competition

Question 1
4 / -1

A body of weight 200 N is suspended form a tree branch thought a chain of mass 10 kg. The branch pulls the chain by a force equal to (if g = 10 m/s²):

A
150 N

B
300 N

C
200 N

D
100 N

Solution

Weight of body = 200 N

Weight of chain = 10 × 10 = 100 N

Chain block system is in equilibrium so

T = 200 + 100 = 300 N.

∴ The Correct answer is Option (2): 300 N
Question 2
4 / -1

A diatomic gas, having C_p = (7/2)R and C_v = (5/2)R, is heated at constant pressure. The ratio dU : dQ : dW

A
3 ∶ 7 ∶ 2

B
5 ∶ 7 ∶ 2

C
5 ∶ 7 ∶ 3

D
3 ∶ 5 ∶ 2

Solution

Since the gas is diatomic and the process is isobaric, we have

⇒ C_p = (7/2)R

⇒ C_v = (5/2)R

⇒ dU = nC_vdT

⇒ dQ = nC_pdT

⇒ dW = nRdT

⇒ dU : dQ : dW

⇒ C_v : C_p : R

⇒ (5/2) R : (7/2) R : R

⇒ 5 ∶ 7 ∶ 2

∴ The ratio dU : dQ : dW is 5: 7: 2
Question 3
4 / -1

Keeping the momentum unchanged, if the mass of a body is doubled, then its kinetic energy

A
remains unchanged

B
gets doubled

C
becomes half

D
increases four times

Solution
Question 4
4 / -1

A body cools down from 50°C to 45°C in 5 minutes and then from 45°C to 40°C in another 8 minutes. The temperature of the surroundings is approximately

A
34°C

B
17°C

C
68°C

D
27°C

Solution
Question 5
4 / -1

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R

Assertion A : In a central force field, the work done is independent of the path chosen

Reason R : Every force encountered in mechanics does not have an associated potential energy.

In the light of the above statements, choose the most appropriate answer from the options given below

A
A is true but R is false

B
Both A and R are true but R is NOT the correct explanation of A

C
Both A and R are true and R is the correct explanation of A

D
A is false but R is true

Solution

Assertion A refers to the property of central force fields, where the work done by such a force is indeed path-independent. This is because the force only depends on the position relative to the center and not the path taken.

Reason R suggests that not all forces in mechanics have an associated potential energy. This is true for certain types of forces, like friction, which do not have a potential energy function in the same way conservative forces do.

Thus, while both statements are true, the reason R does not explain assertion A since central force fields are conservative, and the path independence of work is a feature of conservative forces, not an explanation of the fact that not all forces have potential energy.

Correct answer: Option 2, "Both A and R are true, but R is NOT the correct explanation of A."
Question 6
4 / -1

The equation of simple harmonic progressive wave is given by y = a sin 2π(bt - сx). The maximum particle velocity will be half the wave velocity, if c =

A
2πa

B

C

D
4πa

Solution

General equation of a simple harmonic progressive wave,
Question 7
4 / -1

According to Huygens Principle, the secondary wavefronts are generated from

A
Random points on Primary wavefronts

B
Each points on primary wavefront

C
alternate points on primary wavefront

D
No secondary wavefront are formed

Solution

From the basic features of the Huygens principle, it is clear that each point on the primary wavelet contributes to the formation of secondary wavelets.

So, Each point on the primary wavefront generates a secondary wavefront.
Question 8
4 / -1

Two bodies of equal masses revolve in circular orbits of radii R₁ and R₂ with the sample period. Their centripetal forces are in the ratio.

A

B

C

D

Solution
Question 9
4 / -1

A ball, of mass 0.16 kg, strikes a rigid wall with a speed of 18 km/h and is reflected without any change in speed, as shown in figure. The magnitude of impulse imparted to the ball by the wall is

A
0.4 kg m/s

B
0.8 kg m/s

C
1.4 kg m/s

D
2.4 kg m/s

Solution

Impulse = Change in momentum

Δ P = P_f - P_i

= m (v_f - v_i)

= 0.16(18 - 0)

= 2.88 kg km/h

= 2.88 × 0.27778 kg m/s

= 0.8 kg m/s

The correct answer is option (2).
Question 10
4 / -1

At two particular closest instants of time t₁ and t₂, the displacement of particle performing SHM are equal. At these instants

A
instantaneous speeds are equal

B
instantaneous accelerations are equal

C
kinetic energies are equal

D
all of these
Solution
Instantaneous Speeds
- The speed in SHM is given by,
- v(t) = ω √(A² - x²(t))
- Since the displacement is the same at both t₁ and t₂, and SHM is symmetric about the equilibrium position, the magnitudes of the speed at both times will be the same, but the directions will be opposite.
- Hence, the instantaneous speeds (in terms of magnitude) will be equal.
Instantaneous Accelerations
- The acceleration in SHM is given by,
- a(t) = -ω² x(t)
- Since the displacement x(t₁) = x(t₂), the acceleration at t₁ and t₂ will be the same, both in magnitude and direction.
- Hence, the instantaneous accelerations will be equal.
Kinetic Energies
- The kinetic energy in SHM is given by,
- KE = (1/2) m v²
- Since the speeds (in magnitude) are the same at t₁ and t₂, the kinetic energy, which depends on the square of the speed, will also be the same at both instants.
- Hence, the kinetic energies will be equal.
Therefore, all of these (speeds, accelerations, and kinetic energies) will be equal at the two closest instants when the displacement is the same.

The correct answer is: 4) All of these