Question
Sat June 16, 2012

# A diwali rocket moves vertically up with a constant acceleration of 20/3 ms-2. After sometime its fuel gets exhausted and then it falls freely with an acceleration of 10 ms-2. If the maximum height attained by the diwali rocket is 50m, find its speed when its fuel just gets exhausted..? ans = 20ms-1

Sat June 16, 2012

Let time taken by rocket to finish the fuel be Â‘tÂ’

Since initial velocity u=0m/s

Acceleration of rocket,  a=20/3 ms-2

Let velocity just when fuel gets exhausted be v

Hence using 1st equation of motion:

Distance travelled in that much time t, s1:(using 2nd equation of motion)

Distance travelled upwards after that s2:( using 3rd equation of motion)

Now s1+s2= maximm height attained i.e. 50m

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