Question

On a highway, a car of mass $1.2\times {10}^{3}kg$, travelling at $20m/s$, has kinetic energy equal to that of a loaded van of mass $4.8\times {10}^{3}kg$ travelling with speed $v$. What is the speed of the van ?

• A. $70m/s$
• B. $100m/s$
• C. $10m/s$
• D. $16m/s$

Answer 1

Answer: (C)

$10m/s$

Mass of car $m_1=1.2\times {10}^{3}kg$

Velocity of car $v_1=20m/s$

Mass of van $m_2=4.8\times {10}^{3}kg$

Velocity of van $v_2=?$

Both car as well as van has same kinetic energy.

i.e;$\frac{1}{2}{m}_1{v_1}^2=\frac{1}{2}{m}_2{v_2}^2$

or, $1.2\times {10}^3\times {20}^2=4.8\times {10}^3\times {v_2}^2$

or ${v_2}^2=\frac{400}{4}$

$v_2=10m/s$