Physics Mechanics 5

Question 1

A rigid rod is pivoted at one end. A force of 20 N is applied perpendicular to the rod at a distance of 1.5 m from the pivot. What is the torque produced?

Accepted Answer

30 N·m

Answer

Torque = Force × lever arm = 20 N × 1.5 m = 30 N·m.

Question 2

A 3 kg object falls freely from rest. What is its speed after falling 20 m? (g = 9.8 m/s²)

Accepted Answer

19.8 m/s

Answer

Using v² = 2gh: v = √(2 × 9.8 × 20) = √392 ≈ 19.8 m/s.

Question 3

What is the impulse delivered to a 0.5 kg ball that changes its velocity from 4 m/s to −2 m/s (opposite direction)?

Accepted Answer

−3 N·s

Answer

Impulse = mΔv = 0.5 × (−2 − 4) = 0.5 × (−6) = −3 N·s.

Question 4

Power is defined as the rate of doing work. Which formula correctly expresses power in terms of force and velocity?

Accepted Answer

P = F·v

Answer

Power P = Work/time = (F·d)/t = F·(d/t) = F·v, where v is the velocity of the object.

Question 5

A 0.2 kg ball on a string of length 0.5 m moves in a vertical circle. At the top of the circle, what is the minimum speed needed so the string remains taut?

Accepted Answer

2.21 m/s

Answer

Minimum speed at top: v = √(gr) = √(9.8 × 0.5) = √4.9 ≈ 2.21 m/s.

Physics Practice Test

Physics Practice Test

Physics Mechanics 5