OAR OAR Mechanical Comprehension: Forces 3

Question 1

A 4 kg object is suspended by two ropes that each make a 45° angle with the ceiling. What is the tension in each rope? (g = 10 m/s²)

Accepted Answer

28.3 N

Answer

Each rope's vertical component must support half the weight: T sin 45° = 20 N → T = 20/0.707 ≈ 28.3 N.

Question 2

Which of Newton's laws states that for every action there is an equal and opposite reaction?

Accepted Answer

Third Law

Answer

Newton's Third Law states that action and reaction forces are equal in magnitude and opposite in direction.

Question 3

A car of mass 1,200 kg decelerates from 20 m/s to rest in 4 seconds. What braking force was applied?

Accepted Answer

6,000 N

Answer

a = (0 − 20)/4 = −5 m/s²; F = ma = 1200 × 5 = 6,000 N.

Question 4

Which type of friction acts on an object that is already in motion across a surface?

Accepted Answer

Kinetic friction

Answer

Kinetic (sliding) friction acts on objects in motion and is typically less than static friction.

Question 5

A 60 N force is applied at an angle of 60° above the horizontal to push a box. What is the horizontal component of this force?

Accepted Answer

30 N

Answer

Horizontal component = F cos 60° = 60 × 0.5 = 30 N.

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