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Grade 12IIT JEE Entrance Exam

The kinetic energy of a pulse travelling in a taut string given Tension=10N and mass/unit length=0.1 kg/m is 0.05 K mJ.value of K is what I have to figure out.

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Profile image of Navin
9 Years agoGrade 12
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1 Answer

Profile image of Arun
6 Years ago
At the given time, y = m₁ ⇒ x₀
 
After 't' time, y = m₂x + c ⇒ 0.1 m
 
The mass m₁ is given as:
 
m₁ = 10⁻³/0.1 = 10⁻² kg
 
The mass m₂ is given as:
 
m₂ = 10⁻³/0.05 = 2 × 10⁻² kg
 
The kinetic energy is given as:
 
dK = 1/2 dmV²
 
dK = 1/2 μ.dx (-V. ∂y/∂x)²
 
∫dK = 1/2 μ.V² [m₁² dx + m₂² dx]
 
Now, the velocity is given as:
 
V = √(T/μ)
 
Now, the kinetic energy becomes,
 
K = 1/2 T [m₁² (0.1) + m₂² (0.5)]
 
On substituting the values, we get,
 
K = 1/2 (10) [(10⁻⁴)² (0.1) + (4 × 10⁻⁴)² (0.5)]
 
K = 10/2 [10⁻⁴](0.3)
 
∴ K = 0.15 mJ