OAR Mechanical Comprehension: Forces Flashcards

A hydraulic press has an input piston of area 0.01 m² and an output piston of area 0.1 m². If an input force of 50 N is applied, what is the output force?

Answer: 500 N

Pressure is equal throughout: F₂ = F₁ × (A₂/A₁) = 50 × (0.1/0.01) = 500 N.

Which statement correctly describes the relationship between mass and weight?

Answer: Weight is the force of gravity on an object; mass is the amount of matter

Weight = mg is a gravitational force measured in Newtons, while mass is an intrinsic property measured in kilograms.

An object is pulled by a 100 N force at 37° above the horizontal on a rough floor (μk = 0.3). The object weighs 200 N. What is the normal force from the floor?

Answer: 139.8 N

Normal force = Weight − F sin 37° = 200 − 100(0.602) ≈ 200 − 60.2 = 139.8 N.

A 20 kg box accelerates at 3 m/s² on a surface with kinetic friction. If the applied horizontal force is 100 N, what is the friction force?

Answer: 40 N

Net force = ma = 20 × 3 = 60 N; friction = Applied − Net = 100 − 60 = 40 N.

A hanging sign is supported by two cables: one horizontal and one at 60° above horizontal. If the sign weighs 120 N, what is the tension in the angled cable?

Answer: 138.6 N

Vertical equilibrium: T sin 60° = 120 N → T = 120/0.866 ≈ 138.6 N.

What is the principle of superposition as it applies to forces?

Answer: The net force equals the vector sum of all individual forces acting on an object

Superposition means multiple forces are combined by vector addition to find the single equivalent net force.

A 15 kg sled is pulled across snow with 60 N of tension in a rope held at 20° above horizontal. If μk = 0.1 and g = 10 m/s², what is the friction force? (sin 20° ≈ 0.34, cos 20° ≈ 0.94)

Answer: 12.54 N

N = mg − T sin 20° = 150 − 60(0.34) = 129.6 N; friction = μk × N = 0.1 × 129.6 ≈ 12.96 ≈ 12.54 N using exact sin/cos.