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NEET PHYSICSWORK, ENERGY AND POWEREasy

Question

An engine pumps water continuously through a hose. Water leaves the hose with a velocity vv and mm is the mass per unit length of the water jet. What is the rate at which kinetic energy is imparted to water?

A

12mv3\frac{1}{2}mv^3

B

mv3mv^3

C

12mv2\frac{1}{2}mv^2

D

12m2v2\frac{1}{2}m^2v^2

Step-by-Step Solution

To determine the rate at which kinetic energy is imparted, we must find the Power (PP) delivered by the engine. Power is defined as the rate of change of energy over time (P=dEdtP = \frac{dE}{dt}) .

  1. Kinetic Energy (KE): The kinetic energy of a mass MM moving with velocity vv is given by KE=12Mv2KE = \frac{1}{2}Mv^2 .
  2. Rate of Kinetic Energy: For a continuous jet where velocity vv is constant, the rate of change of kinetic energy is P=d(KE)dt=12v2dMdtP = \frac{d(KE)}{dt} = \frac{1}{2}v^2 \frac{dM}{dt}.
  3. Mass Flow Rate (dMdt\frac{dM}{dt}): We are given the mass per unit length m=dMdlm = \frac{dM}{dl}. In a small interval of time dtdt, the length of the water column leaving the hose is dl=vdtdl = v dt. Therefore, the mass flow rate is: dMdt=dMdldldt=mv\frac{dM}{dt} = \frac{dM}{dl} \cdot \frac{dl}{dt} = m \cdot v
  4. Final Calculation: Substituting the mass flow rate back into the power equation: P=12v2(mv)=12mv3P = \frac{1}{2}v^2 (mv) = \frac{1}{2}mv^3

Thus, the rate at which kinetic energy is imparted to the water is 12mv3\frac{1}{2}mv^3.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from WORK, ENERGY AND POWER. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSWORK, ENERGY AND POWERenginecontinuouslythroughleavesvelocity

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