Question

The work done against gravity in taking 10kg mass at 1m height in 1s will be (in J)
(A) 49
(B) 196
(C) 98
(D) None

Answer 1

Hint We will be calculating total work done by virtue of its position. We are going to use values of mass and height from the question and put it in the formula W=E=mgh. Since it depends on position, the concept of potential energy is also introduced.

Complete Step by step solution

We have to calculate work done in bringing an object at certain height against gravity. This work is stored in the form of energy. That energy is termed as Potential energy.
Potential Energy is defined as the amount of energy required in bringing the body from one position to another position against electrostatic force of attraction. That electrostatic force is acceleration due to gravity.
Mathematically;
Work done (W) = Potential Energy (E) = mgh
According to the question
Mass (m) of an object = 10kg
Height (h) at which it is placed = 1m
Acceleration due to gravity (g) = 9.8 \[\dfrac{m}{{{s^2}}}\] . This value is constant on earth. It changes when the object is on a different planet.
  \[
  {W = 10 \times 9.8 \times 1} \\
  {W = 98\dfrac{{kg{m^2}}}{{{s^2}}}}
\]
W = 98 J

It is a scalar quantity. It depends on initial and final position instead of the path followed.
Option C is the correct option.

Note
We all should be aware of the definition of 1 joule. It is strictly mentioned in the question that the answer should be in joules. Don’t use approximate value of gas 10 \[\dfrac{m}{{{s^2}}}\] instead of 9.8 \[\dfrac{m}{{{s^2}}}\]. If the value of g on different planets is used then might end up with wrong answers.