BARB Mechanical Comprehension 2

Question 1

A wheel has a radius of 0.5 m and rotates at 2 revolutions per second. What is the linear speed of a point on its rim?

Accepted Answer

2π m/s

Answer

Circumference = 2π × 0.5 = π m; Linear speed = π × 2 = 2π m/s.

Question 2

A hydraulic jack has an input piston area of 5 cm² and an output piston area of 50 cm². A 10 N force on the input produces what output force?

Accepted Answer

100 N

Answer

Mechanical advantage = 50 ÷ 5 = 10; Output force = 10 × 10 = 100 N.

Question 3

Two objects are connected by a rope over a frictionless pulley. Object A weighs 8 kg and Object B weighs 5 kg. Which way will the system move?

Accepted Answer

Object A descends

Answer

Object A is heavier (8 kg > 5 kg), so it will descend and Object B will rise.

Question 4

A spring stretches 5 cm when a 10 N force is applied. What force is needed to stretch it 15 cm?

Accepted Answer

30 N

Answer

Spring constant k = 10 ÷ 0.05 = 200 N/m; Force = 200 × 0.15 = 30 N.

Question 5

Gear A (10 teeth) drives Gear B (30 teeth) which is on the same shaft as Gear C (10 teeth). Gear C drives Gear D (20 teeth). If Gear A turns at 300 rpm, what is Gear D's speed?

Accepted Answer

50 rpm

Answer

A→B: 300 × (10/30) = 100 rpm; B and C share a shaft so C = 100 rpm; C→D: 100 × (10/20) = 50 rpm.

BARB - British Army Recruit Battery Practice Test

BARB - British Army Recruit Battery Practice Test

BARB Mechanical Comprehension 2