Force from Speed & Distance — NTSE Physics in 59 Sec ⚡

 

❓ Question

A vehicle starting from rest attains a speed of 72 km/h after covering a distance of 100 m.
If the mass of the vehicle is 500 kg, find the force exerted by the vehicle.

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🖼️ Concept Image

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✍️ Short Solution

This is a pure kinematics + Newton’s second law question.
No tricks, no time calculation — just v² = u² + 2as and F = ma 💯

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🔹 Step 1 — Convert Speed into SI Units (MOST IMPORTANT 💯)

Given speed is in km/h, but formulas need m/s.

$$72\text{ km/h}=20\text{ m/s}$$

📌 NTSE aur school exams mein yahin sabse zyada silly mistakes hoti hain.

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🔹 Step 2 — Write Known Values Clearly

Initial speed:

$$u = 0 \quad \text{(starting from rest)}$$

Final speed:

$$v = 20 \text{ m/s}$$

Distance covered:

$$s = 100 \text{ m}$$

Mass of vehicle:

$$m = 500 \text{ kg}$$

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🔹 Step 3 — Use Equation of Motion

Since u, v, s are given, use:

$$v^2 = u^2 + 2as$$

Substitute values:

$$(20)^2 = 0 + 2a(100)$$
$$400 = 200a$$
$$a = 2 \text{ m/s}^2$$

📌 Acceleration mil gaya — question ab almost done hai ✅

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🔹 Step 4 — Apply Newton’s Second Law

Force is given by:

$$F = ma$$
$$F = 500 \times 2$$
$$F = 1000 \text{ N}$$

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✅ Final Answer

$$\boxed{F = 1000\ \text{N}}$$

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⭐ Golden NTSE Insight

• Jab speed + distance given ho →
  v² = u² + 2as sabse powerful formula hai

• Time nikaalne ki koi zarurat nahi

• Force ke liye hamesha:

$$F = ma$$

🧠 One-line memory:

Speed aur distance mile — time ko ignore karo.