Physics Mechanics Flashcards

A ball is thrown vertically upwards with an initial velocity of 20 m/s. Taking g = 9.8 m/s², what is the maximum height reached?

Answer: 20.4 m

Using v² = u² + 2as where v = 0 at maximum height: 0 = 400 + 2(-9.8)s, so s = 400/19.6 = 20.4 m.

Newton's third law states that when object A exerts a force on object B, object B exerts an equal and opposite force on A. Which of the following is a correct Newton's third law pair?

Answer: The gravitational pull of the Earth on a book and the gravitational pull of the book on the Earth

Newton's third law pairs must act on different objects, be the same type of force, and be equal in magnitude but opposite in direction. The gravitational attraction between Earth and book satisfies all three conditions.

A 2 kg object is accelerated from rest to 10 m/s in 4 seconds. What is the resultant force acting on it?

Answer: 5 N

Acceleration = (10 - 0)/4 = 2.5 m/s². Using F = ma: F = 2 × 2.5 = 5 N.

A projectile is launched horizontally at 15 m/s from a cliff 80 m high. How long does it take to hit the ground? (g = 10 m/s²)

Answer: 4 s

Vertical motion: s = ut + ½gt² where u (vertical) = 0. So 80 = ½ × 10 × t², giving t² = 16, therefore t = 4 s. Horizontal velocity does not affect the time to fall.

What is the moment of a 60 N force applied at 0.8 m from a pivot, at an angle of 30° to the lever arm?

Answer: 24 N m

Moment = Force × perpendicular distance = F × d × sin(θ) = 60 × 0.8 × sin(30°) = 60 × 0.8 × 0.5 = 24 N m.

A car of mass 1200 kg travels at 30 m/s. What is its kinetic energy?

Answer: 540 kJ

KE = ½mv² = ½ × 1200 × 30² = ½ × 1200 × 900 = 540,000 J = 540 kJ.