ECAT — Engineering College Admission Test (UET)
Take the ECAT Physics — Fluid Dynamics, Oscillations and Waves (Set 2): 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. A venturi meter is used to measure:
Answer: C. the speed of a fluid flowing in a pipe
Explanation: It measures the pressure difference between the wide and narrow parts of a pipe, from which Bernoulli's equation gives the flow speed.
Q2. Water flows at 1 m/s through a hose of radius 2 cm, which ends in a nozzle of radius 0.5 cm. With what speed does water leave the nozzle?
Answer: B. 16 m/s
Explanation: A₁v₁ = A₂v₂: v₂ = v₁(r₁/r₂)² = 1 × (2/0.5)² = 16 m/s.
Q3. A raindrop falling through air reaches its terminal velocity when:
Answer: A. the upward drag (plus upthrust) balances its weight
Explanation: At terminal velocity the net force is zero, so the drop moves with constant velocity.
Q4. A sphere of radius 1 mm moves at 0.5 m/s through water (η = 1 × 10⁻³ Pa s). Using Stokes' law, what is the viscous drag on it?
Answer: B. 9.4 × 10⁻⁶ N
Explanation: F = 6πηrv = 6π × 10⁻³ × 10⁻³ × 0.5 = 3π × 10⁻⁶ ≈ 9.4 × 10⁻⁶ N.
Q5. Water leaks from a hole of area 2 cm² in the side of a large open tank, 3.2 m below the water surface. At what rate (volume per second) does water flow out? (g = 10 m/s²)
Answer: B. 1.6 L/s
Explanation: v = √(2gh) = √64 = 8 m/s; flow rate = Av = 2 × 10⁻⁴ × 8 = 1.6 × 10⁻³ m³/s = 1.6 L/s.
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Q6. As the temperature of a liquid such as honey rises, its viscosity:
Q7. Air (density 1.2 kg/m³) flows over the top surface of an aircraft wing at 60 m/s and under the bottom surface at 50 m/s. If the wing area is 20 m², what is the lift force?
Q8. A motion is simple harmonic if the acceleration of the body is:
Q9. A 0.5 kg mass oscillates on a spring of spring constant 50 N/m. What is its frequency of oscillation?
Q10. A particle moves in SHM according to x = 0.05 sin 10t (x in metres, t in seconds). What is its speed when x = 0.03 m?
Q11. A mass on a spring of spring constant 100 N/m oscillates with amplitude 0.2 m. What is the total energy of the oscillation?
Q12. What length must a simple pendulum have to have a period of 2 s? (g = 10 m/s², take π² = 10)
Q13. A simple pendulum hangs in a lift. When the lift accelerates upward, the period of the pendulum:
Q14. In SHM, the phase difference between the displacement and the acceleration of the particle is:
Q15. Food is heated in a microwave oven because microwaves:
Q16. Water waves of frequency 50 Hz have consecutive crests 4 m apart. What is the speed of the waves?
Q17. A stretched wire has a fundamental frequency of 200 Hz. If its tension is increased by a factor of 2.25 (length unchanged), the new fundamental frequency is:
Q18. A string 0.5 m long fixed at both ends carries transverse waves at 300 m/s. What is the frequency of its third harmonic?
Q19. A pipe 0.5 m long is open at both ends. What is the frequency of its first overtone? (speed of sound 340 m/s)
Q20. A pipe closed at one end and a pipe open at both ends have the same length. What is the ratio of their fundamental frequencies (closed : open)?
Q21. Two sound sources sounded together produce 6 beats in 2 s. One has a frequency of 300 Hz. Which of these could be the frequency of the other?
Q22. A motorcyclist rides at 34 m/s straight towards a factory siren of frequency 500 Hz. Taking the speed of sound as 340 m/s, what pitch does the rider hear?
Q23. A train sounds a 720 Hz horn while receding from a person standing on the platform at 20 m/s. Taking the speed of sound as 340 m/s, what pitch does the person hear?
Q24. The speed of sound in a gas at 0 °C is v. At what temperature will the speed be 2v (pressure changes having no effect)?
Q25. If the pressure of air is doubled while its temperature is kept constant, the speed of sound in it:
Q26. In a stationary wave set up by a 680 Hz source, consecutive nodes are 0.25 m apart. What is the speed of the waves?
Q27. Which statement correctly distinguishes a stationary wave from a progressive wave?
Q28. On a progressive wave of wavelength 1.2 m, what is the shortest distance between two points that vibrate with a phase difference of π/3?
Q29. The shock absorbers in a car are an application of:
Q30. Smoke rises more quickly up a chimney when a strong wind blows across its top because: