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Q7.15: NCERT Physics - Part 1 GRAVITATION 7.15 Solution: A body weighs 63 N on the surface of the earth. What is the…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently forget that gravity follows an inverse‑square law and use $g\propto1/(R+h)$ instead of $g\propto1/(R+h)^2$, which gives a weight of $42\,$N rather than the correct $28\,$N. Always square the distance ratio when converting surface weight to a height above the Earth.

A body weighs 63 N on the surface of the earth. What is the gravitational force on it due to the earth at a height equal to half the radius of the earth?

Step-by-Step Verified Solution

**Answer:** 28 N **Step-by-Step Explanation:** Weight at surface W=mg=63W = mg = 63 N. At height h=R/2h = R/2, acceleration due to gravity:
gh=g(RR+h)2=g(RR+R/2)2=g(23)2=4g9g_h = g\left(\frac{R}{R+h}\right)^2 = g\left(\frac{R}{R+R/2}\right)^2 = g\left(\frac{2}{3}\right)^2 = \frac{4g}{9}
Weight at height Wh=mgh=m×4g9=49×63=28 NW_h = mg_h = m \times \frac{4g}{9} = \frac{4}{9} \times 63 = 28 \text{ N}

All Questions in this Chapter

Q7.1 Q7.2 Q7.3 Q7.4 Q7.5 Q7.6 Q7.7 Q7.8 Q7.9 Q7.10 Q7.11 Q7.12 Q7.13 Q7.14 Q7.15 Q7.16 Q7.17 Q7.18 Q7.19 Q7.20 Q7.21

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