Tag: the essence of change

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Questions Related to the essence of change

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

A block of ice at 0 C whose mass is initially 50.0 kg slides along a horizontal surface starting at a speed of 5.38 m/s and finally coming of ice melted as a result of the friction between the block and the surface will be

  1. 2.16 g

  2. 4.0 g

  3. 1 g

  4. 50 g
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Initial KE = 0.5 * 50 * 5.38^2 = 723.6 J. Heat = 723.6 J. Mass melted = Heat / Latent heat = 723.6 / 334,000 J/kg = 0.00216 kg = 2.16 g.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

An ice block is falling from a height. If $75\%$ of the block melts then $h = (g = 10\ ms^{-2})$.

  1. $10.2\ Km$
  2. $12.8\ Km$
  3. $25.2\ Km$
  4. $26.8\ Km$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When an ice block falls and 75 percent of it melts due to friction and thermal conversion, the heat required for melting (Q = m_melt * L_f) comes from the loss of potential energy (m * g * h). Since 75 percent melts, 0.75 * m * L_f = m * g * h. Using the latent heat of fusion of ice (approx 3.34 * 10^5 J/kg) and g = 10, solving for height h yields approximately 25.2 Km.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

A lead ball moving with velocity v strikes a wall and stops. I 50% of its energy is converted into heat, then what will b the increase in temperature? (Specific heat of lead is s)

  1. $\dfrac { 2{ v }^{ 2 } }{ Js } $
  2. $\dfrac { { v }^{ 2 } }{ 4Js } $
  3. $\dfrac { { v }^{ 2 }s }{ J } $
  4. $\dfrac { { v }^{ 2 }s }{ 2J } $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

0.5 * (0.5 * m * v^2) = m * s * delta T * J. 0.25 * m * v^2 = m * s * delta T * J. delta T = v^2 / (4 * J * s).

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

In an energy recycling process, $x _ { g }$ of steam at $100 ^ { \circ } C$ becomes water at $100 ^ { \circ } \mathrm { C }$ which converts $\mathrm { Yg }$ of ice at $0 ^ { \circ } \mathrm { C }$ into water at $100 ^ { \circ } \mathrm { C }$ . The ratio XY will be

  1. $\dfrac { 1 } { 3 }$
  2. $\dfrac { 2 } { 3 }$
  3. $3$
  4. $2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heat released by steam condensing: x * L_v = x * 540 cal. Heat absorbed by ice melting and warming: Y * L_f + Y * 1 * 100 = Y * 80 + Y * 100 = 180Y. Equating: 540x = 180Y. x/Y = 180/540 = 1/3.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

The work done on the particle of mass m by a force $ \overrightarrow { F } =K\left[ \frac { X }{ \left( X^ 2+y^ 2 \right)^{1/2}  } \hat { i } +\frac { y }{ \left( X^ 2+y^ 2 \right)^{1/2}   } \hat { j }  \right]  $ (k being a constant of appropriate simensions), when the particle is taken from the point (a,0) to the point (0,a) along a circular path of radius a about the origin in the X-y plane 

  1. $ \frac {2k\pi}{a} $
  2. $ \frac {k\pi}{a} $
  3. $ \frac {k\pi}{2a} $

  4. 0
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

The maximum amount of work that can be done by extracting $1J$ of energy from a body at $127^oC$ with an environment at $27^oC$?

  1. $\dfrac{1}{8}J$
  2. $\dfrac{1}{4}J$
  3. $\dfrac{1}{2}J$
  4. $\dfrac{3}{4}J$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The maximum work obtainable from a heat engine operating between two temperatures is given by Carnot efficiency: eta = 1 - (T_L / T_H). Here T_H = 127 + 273 = 400 K and T_L = 27 + 273 = 300 K. Thus eta = 1 - (300 / 400) = 1/4 = 0.25. For 1 J of energy extracted from the hot body, the maximum work done is W = eta * Q_H = (1/4) * 1 = 1/4 J.

Multiple choice physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

Which of the following energy conversions take place in a torch?

  1. electrical $\rightarrow$ chemical $\rightarrow$ light
  2. chemical $\rightarrow$ electrical $\rightarrow$ light
  3. electrical $\rightarrow$ light $\rightarrow$ chemical
  4. light $\rightarrow$ chemical $\rightarrow$ electrical
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The chemicalenergy stored in batteries gets transformed into electrical energy through the wires. This then gets transformed into light energy that you see.