Kinematics Question 203
Question: A rocket it’s fired upward from the earth’s surface such that it creates an acceleration of 19.6 m/sec2. If after 5 sec is engine it’s switched off, the maximum height of the rocket from earth’s surface would be [MP PET 1995]
Options:
A) 245 m
B) 490 m
C) 980 m
D) 735 m
Show Answer
Answer:
Correct Answer: D
Solution:
Given $ a=19.6\ m/s^{2}=2g $
Resultant velocity of the rocket after 5 sec $ v=2g\times 5=10g\ m/s $
Height achieved after 5 sec, $ h _{1}=\frac{1}{2}\times 2g\times 25=245m $
On switching off the engine it goes up to height $ h _{2} $ where it’s velocity becomes zero.
$ 0={{(10g)}^{2}}-2gh _{2}\Rightarrow h _{2}=490m $
$ \therefore $ Total height of rocket $ =245+490=735\ m $
