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Work Power and Energy question

2024 · 30 Jan · Shift 2 · Q80
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Work Power and Energy question

2024 · 30 Jan · Shift 2 · Q80

JEE MainPhysicsWork Power and EnergyMCQ+4 / −1
A block of mass 1 kg1 \mathrm{~kg}1 kg is pushed up a surface inclined to horizontal at an angle of 60∘60^{\circ}60∘ by a force of 10 N10 \mathrm{~N}10 N parallel to the inclined surface as shown in figure. When the block is pushed up by 10 m10 \mathrm{~m}10 m along inclined surface, the work done against frictional force is : [g=10 m/s2]\left[g=10 \mathrm{~m} / \mathrm{s}^2\right][g=10 m/s2] JEE Main 2024 (Online) 30th January Evening Shift Physics - Work Power & Energy Question 26 English
  1. A
    5 3\sqrt33​ J
  2. B
    5 J
  3. C
    5×1035\times10^35×103 J
  4. D
    10 J
View written solutionFree

Correct answer: WITH THE GIVEN DATA, THE CORRECT WORK DONE AGAINST FRICTION IS $W=(10-5\SQRT3)\TIMES 10=100-50\SQRT3\,\TEXT{J}\APPROX 13.4\,\TEXT{J}$, SO THE STORED ANSWER B DOES NOT AGREE. IF FORCED TO CHOOSE FROM THE LISTED OPTIONS, THE QUESTION/OPTIONS LIKELY CONTAIN AN ERROR.

  1. Given data

    • Mass of block: m=1 kgm=1\,\text{kg}m=1kg
    • Inclination angle: θ=60∘\theta=60^\circθ=60∘
    • Applied force along incline: F=10 NF=10\,\text{N}F=10N
    • Displacement along incline: s=10 ms=10\,\text{m}s=10m
    • Acceleration due to gravity: g=10 m/s2g=10\,\text{m/s}^2g=10m/s2
  2. Forces along the incline Along the inclined plane:

    • Upward force: applied force F=10 NF=10\,\text{N}F=10N
    • Downward component of weight: mgsin⁡θ=1⋅10⋅sin⁡60∘=10⋅32=53 Nmg\sin\theta = 1\cdot 10\cdot \sin 60^\circ = 10\cdot \frac{\sqrt3}{2}=5\sqrt3\,\text{N}mgsinθ=1⋅10⋅sin60∘=10⋅23​​=53​N
    • Friction acts downward along the plane.
  3. Interpretation of the question Since the options are small and the phrase asks for the work done against frictional force, we take the motion to be at constant speed / no change in kinetic energy, so net force along incline is zero.

    Therefore, F=mgsin⁡θ+fF = mg\sin\theta + fF=mgsinθ+f where fff is the frictional force.

    So, f=F−mgsin⁡θ=10−53f = F - mg\sin\theta = 10 - 5\sqrt3f=F−mgsinθ=10−53​

  4. Work done against friction Work done against friction over distance s=10 ms=10\,\text{m}s=10m is Wf=f s=(10−53)×10W_f = f\,s = (10-5\sqrt3)\times 10Wf​=fs=(10−53​)×10 Wf=100−503W_f = 100 - 50\sqrt3Wf​=100−503​

    Using 3≈1.732\sqrt3\approx 1.7323​≈1.732, Wf≈100−86.6=13.4 JW_f \approx 100 - 86.6 = 13.4\,\text{J}Wf​≈100−86.6=13.4J

  5. Comparison with options The computed value 13.4 J13.4\,\text{J}13.4J does not match any option exactly. The nearest/simple intended value among options is likely 10 J10\,\text{J}10J (Option D) only if the question/data has a typo (for example, displacement or angle).

    With the given data, the exact answer is: 100−503 J\boxed{100-50\sqrt3\,\text{J}}100−503​J​

  6. Conclusion Hence the stored answer B (5 J) is not consistent with the given values.

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