Question

An object, moving with velocity $5\,m / s$, undergoes an acceleration of $1\,m / s ^{2}$ at time $t=0 .$ If the object has a mass of $1\,kg$, the kinetic energy ( KE) of the object at time $t=5\, s$ is

• A. KE = 12.5 J
• B. KE = 20 J
• C. KE = 30 J
• D. KE = 50 J

Answer 1

Answer: (D)

KE = 50 J

Answer 2

Given, $u=5 \,m / s , a=1\, m\,/ s ^{2}$
and mass $=1\, kg$.
So, velocity after $5\,s$ is given as
$v=u+$ at (Equation of motion)
$v=5+1 \times 5$
$\Rightarrow v=10\,m / s$
Kinetic energy of object
$KE =\frac{1}{2} m v^{2}$
$=\frac{1}{2} \times 1 \times(10)^{2}=50\, J$