A fire cracker is fired and it rises to a height of 1000 m. Find the velocity by which it was released and the time taken by it to reach the highest point (take a = 10 m/s?).

Dear student,

(1) h=1000m =S
      v= 0 m/s (at highest point)
       g= 10 m/s2 ( taken to be negative according to sign convention)

Using the 3rd equation  of motion,
v2 - u2 = 2aS0 - u2 =- 2 ×10 ×1000u2 = 20000u = 141.42 m/s

(2) u=141.42 m/s (as calculated above)
1st equation of motion,
V=u+at0=141.42-10t10t=141.42t=14.142 sect=14.1 sec (approx)

velocity by which it is released is 141.42m/s
and time taken to reach the highest point =14.1 sec


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