Physics: Classical Mechanics & Kinematics Flashcards

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)

Answer: 0.5 s

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

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:

Answer: Acts on the rocket in the upward direction

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

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?

Answer: 12 m

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

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?

Answer: 3 m/s

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

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

Answer: 16 m/s²

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

A force of 50 N is applied at 60° to the horizontal to push a crate. What is the horizontal component of the force? (cos60° = 0.5)

Answer: 25 N

Horizontal component = F·cosθ = 50 × 0.5 = 25 N.

Which kinematic equation would you use to find displacement when initial velocity, final velocity, and time are known but acceleration is not needed?

Answer: d = ½(v₀ + v)t

The equation d = ½(v₀ + v)t uses only initial velocity, final velocity, and time.