Question

A rocket is fired upwards. Its velocity versus time graph is shown in fig. The maximum height reached by the rocket is :

• A. $7.2km$
• B. $79.2km$
• C. $72km$
• D. $71km$

Answer 1

The correct option is B $79.2km$

We know, an area under $v-t$ graph gives us displacement .

Here, displacement from $t=0$ to $t=132s$ is same as maximum height reached by the rocket

From the right side triangle :

Base $=132-12=120s$

Height $=1200m/s$

Area$=\frac{1}{2}\times base\times height$

Area $=\frac{1}{2}\times 120\times 1200=72,000m$

Hence, total area $=7,200+72,000=79,200m$

$⟹$ Maximum height reached by the rocket $=79,200m=79.2km$