NCEES Dynamics 2 ā Questions and Answers
Question 1: A 5 kg block slides down a frictionless incline at 30Ā° to the horizontal. What is the acceleration of the block?
- 4.91 m/sĀ² (Correct answer)
- 9.81 m/sĀ²
- 8.50 m/sĀ²
- 2.45 m/sĀ²
Correct answer: 4.91 m/sĀ²
Acceleration = gĀ·sin(30Ā°) = 9.81 Ć 0.5 = 4.91 m/sĀ².
Question 2: A particle undergoes circular motion with radius 2 m and constant speed 6 m/s. What is its centripetal acceleration?
- 18 m/sĀ² (Correct answer)
- 3 m/sĀ²
- 12 m/sĀ²
- 36 m/sĀ²
Correct answer: 18 m/sĀ²
Centripetal acceleration = vĀ²/r = 36/2 = 18 m/sĀ².
Question 3: A 10 kg object is acted upon by a net force of 50 N. What is the resulting acceleration?
- 5 m/sĀ² (Correct answer)
- 0.2 m/sĀ²
- 500 m/sĀ²
- 50 m/sĀ²
Correct answer: 5 m/sĀ²
By Newton's second law, a = F/m = 50/10 = 5 m/sĀ².
Question 4: Two masses, 3 kg and 7 kg, are connected by a string over a frictionless pulley (Atwood machine). What is the acceleration of the system?
- 3.92 m/sĀ² (Correct answer)
- 9.81 m/sĀ²
- 1.96 m/sĀ²
- 6.87 m/sĀ²
Correct answer: 3.92 m/sĀ²
a = (m2ām1)g/(m1+m2) = (7ā3)Ć9.81/10 = 3.92 m/sĀ².
Question 5: A ball is thrown horizontally at 20 m/s from a 80 m high cliff. How long does it take to hit the ground?
- 4.04 s (Correct answer)
- 8.00 s
- 2.02 s
- 1.00 s
Correct answer: 4.04 s
Time = ā(2h/g) = ā(160/9.81) ā 4.04 s; horizontal velocity doesn't affect vertical fall time.
Question 6: A flywheel starts from rest and accelerates uniformly to 600 rpm in 10 seconds. What is its angular acceleration?
- 6.28 rad/sĀ² (Correct answer)
- 60 rad/sĀ²
- 3.14 rad/sĀ²
- 62.8 rad/sĀ²
Correct answer: 6.28 rad/sĀ²
Ļ = 600 rpm Ć 2Ļ/60 = 62.83 rad/s; Ī± = ĪĻ/t = 62.83/10 ā 6.28 rad/sĀ².
Question 7: A 2 kg ball moving at 8 m/s strikes a stationary 6 kg ball in a perfectly inelastic collision. What is the velocity after impact?
- 2 m/s (Correct answer)
- 4 m/s
- 8 m/s
- 1 m/s
Correct answer: 2 m/s
Conservation of momentum: v = m1Ā·v1/(m1+m2) = 2Ć8/8 = 2 m/s.
NCEES Dynamics 2
A 5 kg block slides down a frictionless incline at 30Ā° to the horizontal.
What is the acceleration of the block?