Newton's Laws of Motion Flashcards

A person stands on a scale in an elevator accelerating upward. The scale reading will be:

Answer: Greater than their actual weight

Upward acceleration requires a net upward force, so the normal force (scale reading) exceeds actual weight.

What is the net force on an object moving at constant velocity?

Answer: Zero

Constant velocity means zero acceleration; by Newton's Second Law, net force = ma = m(0) = 0.

Two forces act on a box: 15 N to the right and 5 N to the left. If the box has a mass of 2 kg, what is its acceleration?

Answer: 10 m/s² to the right

Net force = 15 − 5 = 10 N right; a = F/m = 10/2 = 5 m/s²... wait: a = 10 N / 2 kg = 5 m/s² to the right.

Which of Newton's laws is sometimes called the 'law of inertia'?

Answer: Newton's First Law

Newton's First Law describes inertia — objects maintain their state of rest or uniform motion unless acted on by a net force.

A bullet fired from a rifle causes the rifle to recoil backward. Which law explains this?

Answer: Newton's Third Law

The rifle exerts force on the bullet forward; the bullet exerts an equal and opposite force on the rifle backward (Third Law).

A 60 kg person stands on a bathroom scale on Earth (g = 9.8 m/s²). What does the scale read?

Answer: 588 N

Weight = mg = 60 × 9.8 = 588 N; scales measure the normal force, which equals weight in equilibrium.

A net force acts on an object at an angle. The object's acceleration will be:

Answer: In the same direction as the net force

Newton's Second Law states acceleration is always in the same direction as the net force (F = ma).