EIT Dynamics and Vibrations 3 — Questions and Answers
Question 1: A 10 kg block moving at 5 m/s receives an impulse of 60 N·s in the direction of motion. What is the final velocity?
- 6 m/s
- 8 m/s
- 11 m/s (Correct answer)
- 15 m/s
Correct answer: 11 m/s
mv_f = mv_i + J → 10v_f = 10(5) + 60 = 110, so v_f = 11 m/s.
Question 2: A 5 kg object is lifted 10 m vertically. How much work is done against gravity? (g = 9.81 m/s²)
- 50 J
- 196 J
- 490.5 J (Correct answer)
- 981 J
Correct answer: 490.5 J
W = mgh = 5 × 9.81 × 10 = 490.5 J.
Question 3: A 2 kg ball moving at 6 m/s undergoes a perfectly inelastic collision with a stationary 4 kg ball. What is the post-collision velocity?
- 1 m/s
- 2 m/s (Correct answer)
- 3 m/s
- 4 m/s
Correct answer: 2 m/s
m₁v₁ = (m₁ + m₂)v_f → 2(6) = 6v_f, so v_f = 2 m/s.
Question 4: A uniform disk has mass 4 kg and radius 0.5 m. What is its moment of inertia about its central axis?
- 0.25 kg·m²
- 0.50 kg·m² (Correct answer)
- 1.00 kg·m²
- 2.00 kg·m²
Correct answer: 0.50 kg·m²
For a solid disk, I = ½mr² = ½(4)(0.5²) = 0.50 kg·m².
Question 5: A uniform rod (I_cm = mL²/12) has mass 3 kg and length 2 m. What is its moment of inertia about one end?
- 1 kg·m²
- 2 kg·m²
- 4 kg·m² (Correct answer)
- 6 kg·m²
Correct answer: 4 kg·m²
Using the parallel axis theorem: I_end = mL²/12 + m(L/2)² = mL²/3 = 3(4)/3 = 4 kg·m².
Question 6: A motor produces 1500 W at 200 rpm. What torque does it deliver?
- 35.8 N·m
- 71.6 N·m (Correct answer)
- 143.2 N·m
- 300.0 N·m
Correct answer: 71.6 N·m
T = P/ω = 1500 / (200 × 2π/60) = 1500/20.94 ≈ 71.6 N·m.
Question 7: A 0.5 kg ball strikes a wall at 8 m/s and rebounds at 6 m/s. What is the magnitude of the change in momentum?
- 1 kg·m/s
- 4 kg·m/s
- 7 kg·m/s (Correct answer)
- 14 kg·m/s
Correct answer: 7 kg·m/s
|Δp| = m|v_f − v_i| = 0.5 × |−6 − 8| = 0.5 × 14 = 7 kg·m/s.
EIT Dynamics and Vibrations 3
A 10 kg block moving at 5 m/s receives an impulse of 60 N·s in the direction of motion.
What is the final velocity?