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A body of mass \(2 \mathrm{~kg}\) is thrown upward with an energy \(490 \mathrm{~J}\). The height at which its kinetic energy would become half of its initial kinetic energy will be \(\left[g=9.8 \mathrm{~m} / \mathrm{s}^{2}\right.\) ] (a) \(35 \mathrm{~m}\) (b) \(25 \mathrm{~m}\) (c) \(12.5 \mathrm{~m}\) (d) \(10 \mathrm{~m}\)

Short Answer

Expert verified
The height at which the body's kinetic energy would become half of its initial kinetic energy is \(12.5 \mathrm{~m}\). Thus the correct answer is (c) \(12.5 \mathrm{~m}\)

Step by step solution

01

Calculate Initial Kinetic Energy

Given that the energy with which the body is thrown upward is \(490 \mathrm{~J}\), which implies the initial kinetic energy, K.E(_1), of the body is \(490 \mathrm{~J}\).
02

Calculate Final Kinetic Energy

The question states that the kinetic energy would become half of its initial kinetic energy at some height. Thus, the final kinetic energy K.E(_2) = K.E(_1)/2 = \(490/2 = 245 \mathrm{~J}\)
03

Apply Principle of Conservation of Energy

The Principle of Conservation of Energy states that the total initial energy = total final energy. The initial energy (initial kinetic energy, no initial potential energy as the object hadn't climbed any height) is K.E(_1) = \(490 \mathrm{~J}\) and the final energy (final kinetic energy plus potential energy due to climbing) is K.E(_2) + P.E(_2) = \(245 \mathrm{~J} + mgH\). Therefore, \(490 = 245 + 2 * 9.8 * H\).
04

Calculate Height

Isolate the height, H, by subtracting \(245\) from both sides of the equation and then dividing by \(19.6 = 2 * 9.8\). Thus, \(H = (490 - 245)/19.6 = 12.5 \mathrm{~m}\)

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Key Concepts

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

Kinetic Energy
Kinetic energy is the energy that a body possesses by virtue of its motion. It's an essential concept in physics because it helps us understand how moving objects interact. When you throw a ball or when a car speeds down the road, they exhibit kinetic energy. The formula for kinetic energy is:
  • \( \text{Kinetic Energy} = \frac{1}{2} m v^2 \)
where \( m \) is the mass of the object and \( v \) is its velocity. This means that both the mass and velocity of a body play a crucial role in how much kinetic energy it will have.
When the body is thrown upward, as in the exercise, it initially has a maximum amount of kinetic energy derived from the energy supplied to it.
Understanding kinetic energy's role allows us to predict changes in the object's energy states as it moves under the influence of gravity or other forces.
Potential Energy
Potential energy is the energy held by an object due to its position relative to others, stresses within itself, its electric charge, or other factors. In the context of the exercise, we consider gravitational potential energy, as the object is moving against the force of gravity.
  • Gravitational Potential Energy = \( mgh \)
where \( m \) is the mass, \( g \) is the acceleration due to gravity, and \( h \) is the height above the ground.
As the object rises, its kinetic energy converts into potential energy. At the height where its kinetic energy is half of the initial value, the remaining energy has transformed into potential energy, demonstrating how energy is conserved in physical processes.
This transformation is critical in understanding how energy transfers from one form to another without being lost, allowing us to solve various physics problems by applying the conservation principle.
Physics Problems
Solving physics problems often involves using principles like the conservation of energy to predict outcomes and understand natural phenomena. This exercise showcases how energy remains constant in a system, changing forms but not disappearing.
Approaching physics problems requires a systematic method, where identifying given values and known principles is crucial. For instance, in this problem, we had:
  • Total initial energy = initial kinetic energy
  • Total final energy = final kinetic energy + potential energy
By calculating changes in these energy forms, students can determine unknown variables, such as the height at which certain energy criteria are met.
Tackling such problems develops critical thinking and improves the ability to connect theoretical concepts with practical scenarios, a vital skill in physics and beyond.

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Most popular questions from this chapter

A body of mass \(m\) moving with velocity \(v\) makes a head-on collision with another body of mass \(2 m\) which is initially at rest. The loss of kinetic energy of the colliding body (mass \(m\) ) is[MP PMT 1996; RPET 1999; AI (a) \(\frac{1}{2}\) of its initial kinetic energy (b) \(\frac{1}{9}\) of its initial kinetic energy (c) \(\frac{8}{9}\) of its initial kinetic energy (d) \(\frac{1}{4}\) of its initial kinetic energy

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