ECAT — Engineering College Admission Test (UET)
Take the ECAT Physics — Fluid Dynamics, Oscillations and Waves (Set 3): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. Water flows at 2 m/s in a pipe of diameter 10 cm which narrows to diameter 5 cm. The speed in the narrow section is
Answer: C. 8 m/s
Explanation: A₁v₁ = A₂v₂ and A ∝ d², so v₂ = 2 × (10/5)² = 8 m/s.
Q2. A pipe carries water at 4 m/s through an area of 0.02 m². The volume flow rate is
Answer: B. 0.08 m³/s
Explanation: Q = Av = 0.02 × 4 = 0.08 m³/s.
Q3. A large open tank has a small hole 3.2 m below the water surface. The speed of the water leaving the hole is (g = 10 m/s²)
Answer: C. 8 m/s
Explanation: v = √(2gh) = √64 = 8 m/s.
Q4. Water (density 1000 kg/m³) in a horizontal pipe speeds up from 1 m/s to 4 m/s on entering a constriction. The pressure drop is
Answer: A. 7500 Pa
Explanation: ΔP = ½ρ(v₂² − v₁²) = 500 × 15 = 7500 Pa.
Q5. The lift on an aircraft wing is explained mainly by
Answer: B. lower air pressure above the wing than below it
Explanation: Faster flow over the curved top gives lower pressure there (Bernoulli), creating a net upward force.
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Q6. Two identical spheres fall at terminal speed in the same liquid, one with radius r and the other with radius 2r (same material). The ratio of their terminal speeds (larger : smaller) is
Q7. A 0.5 kg mass on a spring of constant 50 N/m oscillates horizontally. Its period is
Q8. A mass hung on a spring stretches it by 0.1 m at equilibrium. Taking g = π² m/s² for convenience, the period of vertical oscillation is
Q9. A simple pendulum has period 2 s on Earth. On a planet where g is four times Earth’s value its period would be
Q10. The length of a simple pendulum that beats seconds (period 2 s) is approximately, with g = π² m/s²,
Q11. A body in SHM has amplitude 5 cm and angular frequency 40 rad/s. Its maximum speed is
Q12. For the same oscillator (A = 5 cm, ω = 40 rad/s) the maximum acceleration is
Q13. A particle in SHM has amplitude A. At the displacement x = A/2 the fraction of the total energy that is kinetic is
Q14. The speed of a particle in SHM of amplitude 0.1 m and ω = 10 rad/s when it is 0.06 m from the mean position is
Q15. Two identical springs of constant k are joined in series and a mass m is hung from them. Compared with a single spring, the period is
Q16. A sound wave of frequency 170 Hz travels at 340 m/s. Its wavelength is
Q17. A string with linear density 0.01 kg/m is under a tension of 160 N. The speed of transverse waves on it is
Q18. A string fixed at both ends has length 0.8 m and wave speed 200 m/s. Its second harmonic has frequency
Q19. A pipe closed at one end has length 0.5 m. With the speed of sound 340 m/s its fundamental frequency is
Q20. A pipe closed at one end can produce which of the following sets of frequencies, in terms of the fundamental f?
Q21. Two tuning forks of frequencies 256 Hz and 260 Hz sound together. The beat frequency and the number of beats in 2.5 s are
Q22. A siren of frequency 800 Hz moves at 20 m/s towards a stationary listener. Taking the speed of sound as 340 m/s, the frequency heard is
Q23. A source of sound moves in a circle at constant speed around a stationary listener at the centre. The listener hears
Q24. The speed of sound in air at 0 °C is 332 m/s. At 27 °C (300 K) it is approximately (using v ∝ √T and 0 °C = 273 K)
Q25. Two points on a progressive wave of wavelength 2 m are 0.5 m apart along the direction of travel. The phase difference between them is
Q26. A swing is pushed in time with its natural frequency and its amplitude grows steadily. This is an example of
Q27. In a damped oscillator, as the oscillations die away, the period of oscillation (for light damping)
Q28. A wave on a string is y = 0.02 sin(4πt − 2πx) in SI units. Its wave speed is
Q29. The nodes of a stationary wave on a string are the points where
Q30. Water flows steadily through a horizontal pipe whose cross-section halves in area. According to Bernoulli’s principle the pressure in the narrow part is