Lift Upward Acceleration Trick — NTSE Physics in 59 Sec ⚡

 

❓ Question

A man of mass 75 kg stands in a lift.
The lift starts moving upward with an acceleration of 2 m/s².
Find the force exerted on him by the floor.

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🖼️ Question Image

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✍️ Short Solution

This is a Newton’s Laws + apparent weight question.
When lift accelerates upward → normal force increases 💯

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🔹 Step 1 — Understand Forces on the Man (MOST IMPORTANT 💯)

Two forces act:

• Upward → Normal Reaction (N)
• Downward → Weight (mg)

Since lift is accelerating upward, net force is upward.

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🔹 Step 2 — Apply Newton’s Second Law

$$N - mg = ma$$

👉 यही सबसे important equation है

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🔹 Step 3 — Substitute Values

Mass:

$$m = 75 \text{ kg}$$

Acceleration:

$$a = 2 \text{ m/s}^2$$

Take:

$$g = 10 \text{ m/s}^2$$
$$N - (75 \times 10) = 75 \times 2$$
$$N - 750 = 150$$
$$N = 900 \text{ N}$$

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🔹 Step 4 — Interpret the Result

👉 Normal force = apparent weight
👉 Lift upward acceleration ⇒ weight increases

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✅ Final Answer

$$\boxed{900\ \text{N}}$$

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⭐ Golden NTSE Insight

• Lift upward acceleration:

$$N = m(g + a)$$

• Lift downward acceleration:

$$N = m(g - a)$$

• Free fall:

$$N = 0$$

🧠 One-line memory:

Lift upar → weight heavy | Lift neeche → weight light