Question

Adjacent graph shows the variation of velocity of a rocket with time. Find the time of burning of fuel from the graph $(g=10m/s^2)$

• A. $10$ $sec$
• B. $110$ $sec$
• C. $120$ $sec$
• D. Cannot be estimated from the graph

Answer 1

The correct option is A $10$ $sec$

Fuel burnt simply means that the $Force$ by engine is $zero$

thus the acceleration will be $zero$

in other words the $velocity$ will $stop$ from $increasing$ and due to $gravity$ $\left(downward\right)$ it will start $decreasing$

so the slope $(acceleration=a=\frac{d}{dt}v=slope)$ will become $negative$.

Observing the graph we find that at $t=10second$ the slope beacame $negative$ thus velocity started $decreasing$.

So time for burning of fuel was just $10s$