AP Physics Physics: Classical Mechanics & Kinematics 3

Question 1

A ball rolls off a horizontal table of height 1.25 m with a horizontal speed of 3 m/s. How long does it take to hit the ground? (g = 10 m/s²)

Accepted Answer

0.5 s

Answer

Using h = ½gt²: 1.25 = ½(10)t², so t² = 0.25, t = 0.5 s.

Question 2

Newton's third law states that for every action there is an equal and opposite reaction. When a rocket expels gas downward, the reaction force:

Accepted Answer

Acts on the rocket in the upward direction

Answer

The expelled gas pushes down (action), and by Newton's third law the rocket is pushed upward (reaction).

Question 3

An object moves with velocity described by v(t) = 4t − 2 m/s. What is the displacement from t = 1 s to t = 3 s?

Accepted Answer

12 m

Answer

Displacement = ∫₁³ (4t−2)dt = [2t²−2t]₁³ = (18−6)−(2−2) = 12 − 0 = 12 m.

Question 4

A 3 kg object moving at 6 m/s collides with a stationary 3 kg object and they stick together. What is their final velocity?

Accepted Answer

3 m/s

Answer

By conservation of momentum: (3)(6) = (3+3)v, so v = 18/6 = 3 m/s.

Question 5

What is the centripetal acceleration of an object moving in a circle of radius 4 m at a speed of 8 m/s?

Accepted Answer

16 m/s²

Answer

Centripetal acceleration a_c = v²/r = 64/4 = 16 m/s².

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