A block of mass 10 kg, moving in x direction with a constant speed of 10 m s ⁻¹, is subjected to a retarding force F = 0.1x J/m during its travel from x = 20 m to 30 m. Its final KE will be (a) 275 J (b) 250 J (c) 475 J (d) 450 J

Answer: (c). Initial KE = 1/2(10)(10)² = 500 J Work by retarding force W = -∫₂₀³⁰ 0.1x dx = -0.05(900 - 400) = -25 J Final KE = 500 - 25 = 475 J So the answer is (c) 475 J.

A block of mass 10 kg, moving in x direction with a constant speed of… | NEET 2015 (AIPMT, Cancelled Paper)

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Work by a Variable Force

A block of mass 10 kg, moving in x direction with a constant speed of 10 m s ${}^{-1}$ , is subjected to a retarding force F = 0.1x J/m during its travel from x = 20 m to 30 m. Its final KE will be

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Answer: (c)

Initial KE $= \frac{1}{2}(10)(10)^2 = 500$ J
Work by retarding force $W = -\int_{20}^{30} 0.1x\,dx = -0.05(900 - 400) = -25$ J
Final KE $= 500 - 25 = 475$ J
So the answer is (c) 475 J.

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