Verified Solution • 2025–26 Session moderate

QJEEM21Phca26: JEE Main 2021 Physics - Class 11 JEEM21Phca26 Solution: A block moving horizontally on a smooth surface with a speed of …

A block moving horizontally on a smooth surface with a speed of 40 m/s splits into two parts with masses in the ratio of 1 : 2. If the smaller part moves at 60 m/s in the same direction, then the fractional change in kinetic energy is :-

Multiple Choice Options

  • A 13{{1 \over 3}}
  • B 23{{2 \over 3}}
  • C 18{{1 \over 8}}
  • D 14{{1 \over 4}}

Step-by-Step Verified Solution

JEE Main 2021 (Online) 31st August Evening Shift Physics - Work Power & Energy Question 68 English Explanation
3MV0 = 2MV2 + MV1

3V0 = 2V2 + V1

120 = 2V2 + 60 ⇒\Rightarrow V2 = 30 m/s

ΔK.E.K.E.=12MV12+122MV22−123MV02123MV02{{\Delta K.E.} \over {K.E.}} = {{{1 \over 2}MV_1^2 + {1 \over 2}2MV_2^2 - {1 \over 2}3MV_0^2} \over {{1 \over 2}3MV_0^2}}

=V12+2V22−3V023V02= {{V_1^2 + 2V_2^2 - 3V_0^2} \over {3V_0^2}}

=3600+1800−48004800=18= {{3600 + 1800 - 4800} \over {4800}} = {1 \over 8}

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