Question

A body of mass 5kg, initially at rest, is subjected to a force of 20N. What is the kinetic energy acquired by the body at the end of 10 s?
(A). 2000 J
(B). 4000 J
(C). 8000 J
(D). 1000 J

Answer 1

Hint: - For solving this type of question we must know the definition of Kinetic energy and Force. And also, the equation of motion is very important.
Formula used: $v= u+at $ and K.E = $\dfrac{1}{2}{{m}{{v^2}}}$

Complete step-by-step solution -
The kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its given velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes.
SI unit of kinetic energy is Joule (J) also, ${E_k} = \dfrac{1}{2}m{v^2}$
Force can be described intuitively as a push or a pull. Force is any interaction that, when unopposed, will change the motion of an object. A force can cause an object with mass to change its velocity, i.e., to accelerate. A force has both magnitude and direction which makes it a vector quantity.
SI Unit of force is $\text{Kg}\times {{m}/{s^2}}$
We have mass of the body, m=5kg,
Initial velocity of the body, u=0;
Force acting on the body, F=20N;
Time for which the force acts, t=10s
If a is the acceleration produced in the body,
$a= \dfrac{F}{m} = \dfrac{20}{5} = 4 m/{s^2}$
Let $v$ be the velocity of the body after 10 s.
By the formula $v = u + at$
We have $v = 0+\text{4}\times{\text{10}}$
Therefore the Kinetic energy acquired by the body is
${E_k} = \dfrac{1}{2}m{v^2} = \dfrac{1}{2}(5) \times {(40)^2} = 4000J$
Hence option B is the correct answer.

Note: - For solving such types of questions we must know how to solve the motion equation also the properties related to speed. Also we must keep in our mind that the value of each term must be in the same unit.