Tag: physics

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Questions Related to physics

Multiple choice physics energy : forms and sources concept of energy energy for everything forms of energy

An object of mass $40\ kg$ is raised to a height of $5\ m$ above ground. If the object is allowed to fall down find its kinetic energy when it is half-way down.

  1. 1960 J

  2. 980 J

  3. 990 J

  4. 1000 J
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Gravitational Potential energy, $W = mgh$

$h=$ vertical displacement $=5\ m$

$m =$ Mass of object $= 40\ Kg$

$g =$ Acceleration due to gravity $= 9.8\ ms^{-2}$

$W = 40 \times 5 \times 9.8= 1960\ J$

For half way down$=\dfrac{1960}{2}= 980\ J$

At this point i.e. half way object has an equal amount of potential and kinetic energy.

Multiple choice physics energy : forms and sources concept of energy energy for everything forms of energy

A certain household has consumed $250$ units of energy during a month. How much energy is this in joules?

  1. $9 \times 10^{10}\ J$
  2. $9 \times 10^{8}\ J$
  3. $9 \times 10^{9}\ J$
  4. $9 \times 10^{-8}\ J$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$1$ unit of energy $=1\ kWh$

$1\ kwh=3.6 \times 10^{6}\ J$

Thus $250$ unit$=250 \times 3.6 \times 10^{6}\ J$$=9 \times 10^{8}\ J$

Multiple choice physics energy : forms and sources concept of energy energy for everything forms of energy

Energy equivalent of 4.2 mg in kilo calories is

  1. $9 \times 10^{10} cal$
  2. $8 \times 10^{8} cal$
  3. $10 \times 10^{9} cal$
  4. $6 \times 10^{7} cal$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Using E = mc^2. m = 4.2 mg = 4.2 * 10^-6 kg. c = 3 * 10^8 m/s. E = 4.2 * 10^-6 * (9 * 10^16) = 37.8 * 10^10 J. Converting to calories (1 cal = 4.184 J), the result is approximately 9 * 10^10 cal.