A 60kg man stands on a weighing balance in an elevator. If the elevator accelerates upwards at 5ms$^{-2}$, determine the reading of the scale. [g = 10ms$^{-2}$]

Analyze the question: A man stands on a scale in a lift accelerating upwards. The scale reads the normal reaction force R, which is the force the scale exerts on the man.

Concept: When a lift accelerates upwards, the scale must push up with more force than the man's weight, so he feels "heavier". Apply Newton's second law:

R − mg = ma, so R = m(g + a)

Solution:

• Mass, m = 60 kg
• g = 10 m/s²
• a = 5 m/s² (upwards)

Weight = mg = 60 × 10 = 600 N

Net force needed = ma = 60 × 5 = 300 N

R = mg + ma = 600 + 300 = 900 N

Answer: D. 900N

Tip: Remember the pattern for lift problems:

• Accelerating up (or decelerating while moving down): R = m(g + a), so the reading is larger.
• Accelerating down (or decelerating while moving up): R = m(g − a), so the reading is smaller.
• Constant velocity or at rest: R = mg.

Option B (600 N) is the trap for students who forget the lift's acceleration, and option A (300 N) is just ma on its own.