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A body is moving unidirectionally under the influence of a source of constant power. Its displacement in time \(t\) is proportional to (i) \(t^{1 / 2}\) (ii) \(t\) (iii) \(t^{3 / 2}\) (iv) \(t^{2}\)

Short Answer

Expert verified
(iii) \(t^{3/2}\)

Step by step solution

01

Understanding the Problem

We need to determine how the displacement of the body changes with time given a constant power source. We know that power is the rate at which work is done or energy is transferred, which is constant in this case.
02

Relate Power to Kinetic Energy

Power (P) is related to kinetic energy (K.E.) as \( P = \frac{dK.E.}{dt} \). With constant power, \( P \cdot t = K.E. \) , so \( Pt = \frac{1}{2}mv^2 \) where \( m \) is mass and \( v \) is velocity.
03

Solve for Velocity

From \( Pt = \frac{1}{2}mv^2 \), rearrange to find the velocity: \( v^2 = \frac{2Pt}{m} \). Therefore, \( v = \sqrt{\frac{2Pt}{m}} \).
04

Find Displacement as a Function of Time

Velocity is the derivative of displacement \( x \), \( v = \frac{dx}{dt} \). Substitute the derived velocity: \( \frac{dx}{dt} = \sqrt{\frac{2Pt}{m}} \).
05

Separate and Integrate to Find x(t)

Rearrange to integrate: \( dx = \sqrt{\frac{2P}{m}}t^{1/2} \cdot dt \), integrate both sides to find \( x(t) \): \( x = \int \sqrt{\frac{2P}{m}} \cdot t^{1/2} dt = \frac{2\sqrt{2P/m}}{3} \cdot t^{3/2} + C \), where \( C \) is the constant of integration.
06

Conclusion

The displacement \( x(t) \) is proportional to \( t^{3/2} \), therefore, option (iii) is correct.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Displacement Proportionality
Understanding how displacement is related to time is crucial when dealing with motion influenced by a constant power source. In this context, displacement refers to the distance a body moves over time.
For constant power scenarios, the relationship between displacement and time can often be expressed through a mathematical power function of time. Here, we're interested in finding the correct power or exponent that accurately describes this relationship.
To do this, we engaged in the process of analyzing the connection between kinetic energy and time to infer the function that best represents displacement. In our solution, we deduced that the displacement is proportional to \( t^{3/2} \). This means that if we were to graph displacement against time, the shape of the graph would resemble the curve defined by \( t^{3/2} \).
This proportionality shows us that displacement does not increase linearly, but rather at a rate where the influence of time is more pronounced as it increases. This is a common characteristic when a constant power source governs a body's movement, leading to nonlinear increases in displacement over time.
Kinetic Energy and Velocity Relationship
The relationship between kinetic energy and velocity plays a central role in understanding how an object's motion evolves under constant power. Power, defined as the rate at which work is done, is directly tied to changes in kinetic energy.
When we consider a body moving with constant power, the equation \( P = \frac{dK.E.}{dt} \) translates to the kinetic energy increasing proportionally with time. Since kinetic energy is expressed as \( \frac{1}{2}mv^2 \), we can equate and solve for velocity: \( v^2 = \frac{2Pt}{m} \), leading to \( v = \sqrt{\frac{2Pt}{m}} \).
This expression indicates that velocity itself is not constant but increases as the square root of time due to the continuous input of power. It highlights the inherent dynamic nature of velocity, tied both to the steady supply of power and the resultant kinetic energy changes.
  • Velocity and time: As time progresses, velocity increases.
  • Kinetic energy growth: Directly linked with constant power supply.
This relationship aids in deducing how the velocity alters displacement, showcasing why displacement ultimately correlates with \( t^{3/2} \) rather than a simpler linear or quadratic relationship.
Integration in Physics Problems
In physics, integration is a powerful mathematical tool that helps solve problems involving variables that change over time. It comes into play prominently when linking velocity and displacement.
Given the equation \( \frac{dx}{dt} = \sqrt{\frac{2Pt}{m}} \), finding displacement \( x(t) \) as a function of time involves integrating this expression with respect to time.
By separating variables and integrating each side, we arrive at the integral \( \int dx = \int \sqrt{\frac{2P}{m}} \cdot t^{1/2} dt \). The solution to this integral provides us: \( x = \frac{2\sqrt{2P/m}}{3} \cdot t^{3/2} + C \), where \( C \) is the constant of integration.
  • Integration process: Essential for evolving from velocity to displacement.
  • Constant of integration: Represents initial conditions or starting point.
This calculation shows that integration is not just a mathematical operation but a crucial strategy for bridging instantaneous rates of change (like velocity) with cumulative quantities (such as displacement) in physics problems.

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Most popular questions from this chapter

A person trying to lose weight (dieter) lifts a \(10 \mathrm{~kg}\) mass, one thousand times, to a height of \(0.5 \mathrm{~m}\) each time. Assume that the potential energy lost each time she lowers the mass is dissipated. (a) How much work does she do against the gravitational force ? (b) Fat supplies \(3.8 \times 10^{7} \mathrm{~J}\) of energy per kilogram which is converted to mechanical energy with a \(20 \%\) efficiency rate. How much fat will the dieter use up?

The bob of a pendulum is released from a horizontal position. If the length of the pendulum is \(1.5 \mathrm{~m}\), what is the speed with which the bob arrives at the lowermost point, given that it dissipated \(5 \%\) of its initial energy against air resistance?

An electron and a proton are detected in a cosmic ray experiment, the first with kinetic energy \(10 \mathrm{keV}\), and the second with \(100 \mathrm{keV}\). Which is faster, the electron or the proton ? Obtain the ratio of their speeds. (electron mass \(=9.11 \times 10^{-31} \mathrm{~kg}\). proton mass \(\left.=1.67 \times 10^{-27} \mathrm{~kg} .1 \mathrm{eV}=1.60 \times 10^{-19} \mathrm{~J}\right]\)

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A body of mass \(0.5 \mathrm{~kg}\) travels in a straight line with velocity \(v=a x^{3 / 2}\) where \(a=5 \mathrm{~m}^{-1 / 2} \mathrm{~s}^{-1}\). What is the work done by the net force during its displacement from \(x=0\) to \(x=2 \mathrm{~m} ?\)

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