Question

Displacement of an object of mass $2kg$ varies as $s=3t^2+5$. Find out the value of workdone on the mass from $t=0$ to $t=5$ seconds.

• A. $100J$
• B. $200J$
• C. $500J$
• D. $900J$

Answer 1

The correct option is D $900J$

Velocity of the object:
$V=\frac{ds}{dt}=6t$
At $t=0$,
$V_0=0m/s$
At, $t=5s$
$V_5=6\times 5=30m/s$

Initial kinetic energy $K_i=\frac{1}{2}\times 2\times (V_0{)}^2$
Initial kinetic energy $K_i=\frac{1}{2}\times 2\times (0{)}^2=0$

Final kinetic energy $K_f=\frac{1}{2}\times 2\times (V_5{)}^2$
Final kinetic energy $K_f=\frac{1}{2}\times 2\times (30{)}^2=900J$

We know, from work energy theorem:
$W=K_f-K_i=900J$