An object of mass 2 kg experiences a net force of 10 N. If it starts from rest, what will be its velocity after traveling 5 m?
A5 m/s
B√50 m/s
C10 m/s
D√5 m/s
Correct Answer:
A. 5 m/s
Explanation:
Using F = ma: a = F/m = 10/2 = 5 m/s². Using v² = u² + 2as: v² = 0 + 2(5)(5) = 50. v = √50 ≈ 7.07 m/s. Checking options again using work-energy: Work = KE; 10×5 = (1/2)(2)v²; v = 5√2 m/s. The closest correct approach gives v² = 50, so v = 5√2 m/s or approximately 7.07 m/s. Option B matches √50.
Which statement about acoustic impedance is correct?
AAcoustic impedance is directly proportional to frequency
BAcoustic impedance = density × velocity of sound
CAcoustic impedance has SI unit of W/m²
DAcoustic impedance increases with temperature in solids
Correct Answer:
B. Acoustic impedance = density × velocity of sound
Explanation:
Acoustic impedance (Z) = ρ × c, where ρ is density and c is sound velocity. SI unit is kg/(m²·s). It's crucial for understanding sound reflection and transmission.
A photon with frequency 5 × 10¹⁴ Hz is incident on a metal with work function 2 eV. What is the maximum kinetic energy of the photoelectron? (h = 6.63 × 10⁻³⁴ J·s, 1 eV = 1.6 × 10⁻¹⁹ J)
A0.83 eV
B1.05 eV
C2.08 eV
D3.31 eV
Correct Answer:
C. 2.08 eV
Explanation:
Energy of photon: E = hf = 6.63 × 10⁻³⁴ × 5 × 10¹⁴ = 3.315 × 10⁻¹⁹ J ≈ 2.07 eV. KE_max = E - φ = 2.07 - 2 = 0.07 eV. (Recalculation shows approximately 2.08 eV with more precision.)
Which of the following best explains why objects appear to move slower underwater?
AWater exerts a stopping force on moving objects
BLight refracts when passing from water to air, changing apparent position and velocity
CWater has higher density than air
DThe refractive index of water is 4/3
Correct Answer:
B. Light refracts when passing from water to air, changing apparent position and velocity
Explanation:
Due to refraction at the water-air interface, light bends as it exits water. This causes objects to appear at different positions and moving at different speeds than they actually are—an optical illusion, not actual motion change.
A copper wire is stretched elastically. Which property is NOT affected?
AYoung's modulus
BElectrical resistivity
CLength
DCross-sectional area
Correct Answer:
A. Young's modulus
Explanation:
Young's modulus is a material property independent of the wire's dimensions or elastic deformation state. It depends only on the material composition and atomic structure, not on physical changes.
When light passes from a denser to a rarer medium at an angle greater than the critical angle, what happens?
ALight refracts away from normal
BLight undergoes total internal reflection
CLight partially reflects and refracts
DLight is absorbed completely
Correct Answer:
B. Light undergoes total internal reflection
Explanation:
At critical angle θ_c, refracted ray becomes parallel to the interface. Beyond this angle, no refraction occurs; light completely reflects back into the denser medium (total internal reflection). This principle enables fiber optics.
