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Work Power and Energy question

2025 · 7 Apr · Shift 1 · Q53
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Work Power and Energy question

2025 · 7 Apr · Shift 1 · Q53

JEE MainPhysicsWork Power and EnergyMCQ+4 / −1
An object of mass 1000 g experiences a time dependent force F⃗=(2ti^+3t2j^)N\vec{F}=\left(2 t \hat{i}+3 t^2 \hat{j}\right) NF=(2ti^+3t2j^​)N. The power generated by the force at time ttt is:
  1. A
    (2t2+18t3)W\left(2 t^2+18 t^3\right) W(2t2+18t3)W
  2. B
    (3t3+5t5)w\left(3 t^3+5 t^5\right) w(3t3+5t5)w
  3. C
    (2t3+3t5)w\left(2 t^3+3 t^5\right) w(2t3+3t5)w
  4. D
    (2t2+3t3)w\left(2 t^2+3 t^3\right) w(2t2+3t3)w
View written solutionFree

Correct answer: C

  1. Given data
  • Mass of the object: 1000 g=1 kg1000\,\text{g} = 1\,\text{kg}1000g=1kg
  • Force: F⃗=(2t i^+3t2 j^) N\vec F = (2t\,\hat i + 3t^2\,\hat j)\,\text{N}F=(2ti^+3t2j^​)N

We need power at time ttt.

  1. Use Newton's second law to find acceleration

Since F⃗=ma⃗\vec F = m\vec aF=ma and m=1 kgm=1\,\text{kg}m=1kg, a⃗=F⃗=2t i^+3t2 j^\vec a = \vec F = 2t\,\hat i + 3t^2\,\hat ja=F=2ti^+3t2j^​

So, ax=2t,ay=3t2a_x = 2t, \qquad a_y = 3t^2ax​=2t,ay​=3t2

  1. Find velocity by integrating acceleration

Assuming the object starts from rest at t=0t=0t=0,

For xxx-component: vx=∫2t dt=t2v_x = \int 2t\,dt = t^2vx​=∫2tdt=t2

For yyy-component: vy=∫3t2 dt=t3v_y = \int 3t^2\,dt = t^3vy​=∫3t2dt=t3

Hence, v⃗=t2 i^+t3 j^\vec v = t^2\,\hat i + t^3\,\hat jv=t2i^+t3j^​

  1. Use power formula

Instantaneous power is P=F⃗⋅v⃗P = \vec F \cdot \vec vP=F⋅v

So, P=(2t i^+3t2 j^)⋅(t2 i^+t3 j^)P = (2t\,\hat i + 3t^2\,\hat j) \cdot (t^2\,\hat i + t^3\,\hat j)P=(2ti^+3t2j^​)⋅(t2i^+t3j^​)

P=2t⋅t2+3t2⋅t3P = 2t \cdot t^2 + 3t^2 \cdot t^3P=2t⋅t2+3t2⋅t3

P=2t3+3t5P = 2t^3 + 3t^5P=2t3+3t5

Thus, P=(2t3+3t5) W\boxed{P = (2t^3 + 3t^5)\,\text{W}}P=(2t3+3t5)W​

  1. Compare with options
  • A: (2t2+18t3)(2t^2+18t^3)(2t2+18t3) ❌
  • B: (3t3+5t5)(3t^3+5t^5)(3t3+5t5) ❌
  • C: (2t3+3t5)(2t^3+3t^5)(2t3+3t5) ✅
  • D: (2t2+3t3)(2t^2+3t^3)(2t2+3t3) ❌

Therefore, the correct option is C.

  1. Comparison with stored answer

Stored correct answer: C

Our derived answer also gives C, so they agree.

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