NCEES Dynamics 4

Question 1

A disk has mass 10 kg and radius 0.5 m. What is its mass moment of inertia about its central axis?

Accepted Answer

1.25 kg·m²

Answer

I = ½mr² = ½ × 10 × 0.25 = 1.25 kg·m² for a solid disk.

Question 2

What does the work-energy theorem state for a particle?

Accepted Answer

Net work equals the change in kinetic energy

Answer

The work-energy theorem states that the net work done on a particle equals its change in kinetic energy.

Question 3

A 1500 kg car traveling at 30 m/s brakes to a stop over 60 m. What is the average braking force?

Accepted Answer

11,250 N

Answer

Using work-energy: F = ΔKE/d = (½×1500×900)/60 = 675000/60 = 11,250 N.

Question 4

In a central-force problem, which quantity is conserved along the orbit?

Accepted Answer

Angular momentum

Answer

For a central force, the torque about the center is zero, so angular momentum is conserved.

Question 5

The parallel-axis theorem relates the moment of inertia about an axis through the centroid (Ī) to a parallel axis at distance d as:

Accepted Answer

I = Ī + md²

Answer

The parallel-axis theorem is I = Ī + md², where m is mass and d is the distance between axes.

NCEES Practice Test