Question

An object of mass 1000kg is travelling with a velocity 72km/h.Calculate the work done to bring it to rest

Answer 1

According to work - energy theorem,

$\displaystyle\longrightarrow\sf{W=K_f-K_i}$

$\displaystyle\longrightarrow\sf{W=\dfrac{1}{2}m(v^2-u^2)}$

Here,

• $\displaystyle\sf{m=1000\ kg}$

• $\displaystyle\sf{u=72\ km\ h^{-1}=20\ m\ s^{-1}}$

• $\displaystyle\sf{v=0\ m\ s^{-1}}$

Then,

$\displaystyle\longrightarrow\sf{W=\dfrac{1}{2}\times1000(0^2-20^2)}$

$\displaystyle\longrightarrow\sf{\underline{\underline{W=-200\ kJ}}}$

The negative shows that the force should be given in the direction opposite to the motion of the object.