Question

Passage:-

rocket is fired from ground level vertically upward as it move of its speed time graph is shown below


1) fuel gets exhausted at

1. 0s
2. 10s
3. 20s
4. 120s

2) rocket travel after fuel exhausted

1. vertically upward forever

2. vertically upward for sometime

3. vertically upward till 20s

4. first upward and downward till 120s

3). find speed time relation of rocket before and after fuel get exhausted

4). find maximum height reached by rocket above ground

Answer 1

The distance travelled by the rocket during burning interval (1 min = 60 sec.) in which resultant acceleration is vertically upwards and 10 m/s2 will be

 

h = u*t + 1/2 g*t²

h = 0* 60 + 1/2 *10 *60²

h = 1800 m

 

Now the velocity acquired will be-

V = u + a*t

V = 0+ 10 *60 = 600 m/sec

 

As after burning of fuel the initial velocity from (ii) is 600 m/s and gravity opposes the motion of rocket, so from 1 st equation of motion time taken by it to reach the  maximum height (for which v = 0)

 v = u – gt

 0 = 600 – 10t

 t = 60 sec