arthham

JEE Advanced 2012 · Work, Energy and Power

This question has statement I and statement II. Of the four choices given after the statements, choose the one that best describes the two statements. Statement - I: A point particle of mass mm moving with speed vv collides with stationary point particle of mass MM. If the maximum energy loss possible is given as f(12mv2)f(\frac{1}{2}mv^2) then f=(m/(M+m))f=(m/(M+m)). Statement - II: Maximum energy loss occurs when the particles get stuck together as a result of the collision.

Answer: D. Statement - I is false, Statement - II is true.

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Written solution

Step 1: Analyze Statement II and the condition for maximum energy loss.

The maximum loss of kinetic energy in a collision occurs when the collision is perfectly inelastic, meaning the particles stick together after the collision.

Thus, Statement II is true.

Step 2: Apply conservation of linear momentum for a perfectly inelastic collision.

Let uu be the common velocity of the combined mass (m+M)(m + M) after the collision.

mv=(m+M)umv = (m + M)u u=mvm+Mu = \frac{mv}{m + M}

Step 3: Calculate the final kinetic energy.

Substitute the expression for uu into the kinetic energy formula.

KEf=12(m+M)u2KE_f = \frac{1}{2}(m + M)u^2 KEf=12(m+M)(mvm+M)2KE_f = \frac{1}{2}(m + M)\left(\frac{mv}{m + M}\right)^2 KEf=(12mv2)(mm+M)KE_f = \left(\frac{1}{2}mv^2\right)\left(\frac{m}{m + M}\right)

Step 4: Calculate the maximum energy loss.

The maximum energy loss ΔKEmax⁡\Delta KE_{\max} is the difference between the initial and final kinetic energies.

ΔKEmax⁡=KEi−KEf\Delta KE_{\max} = KE_i - KE_f ΔKEmax⁡=12mv2−(12mv2)(mm+M)\Delta KE_{\max} = \frac{1}{2}mv^2 - \left(\frac{1}{2}mv^2\right)\left(\frac{m}{m + M}\right) ΔKEmax⁡=(12mv2)(1−mm+M)\Delta KE_{\max} = \left(\frac{1}{2}mv^2\right)\left(1 - \frac{m}{m + M}\right) ΔKEmax⁡=(12mv2)(Mm+M)\Delta KE_{\max} = \left(\frac{1}{2}mv^2\right)\left(\frac{M}{m + M}\right)

Step 5: Determine the fraction ff and evaluate Statement I.

Comparing the maximum energy loss to the given expression f(12mv2)f\left(\frac{1}{2}mv^2\right) yields the value of ff.

f=Mm+Mf = \frac{M}{m + M}

Since Statement I claims f=mM+mf = \frac{m}{M+m}, Statement I is false.

Answer: Statement - I is false, Statement - II is true.

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