Question

A firecracker is thrown downward from a height of 2.75m above the ground, with a speed of 3.15m/s. Ignore air resistance, determine the height above the ground that the firecracker would be moving at 5.23m/s.

Answer 1

Here in this question as we can see there is no air friction so we can use the principle of energy conservation

`PE_i + KE_i = PE_f + KE_f`

`mgh_1 + (1)/(2)mv_i^2 = mgh_2 + (1)/(2)mv_f^2`

now here we know that

`h_1 = 2.75 m`

`v_i = 0`

`v_f = 5.23 m/s`

now plug in all values in above equation

`mg*2.75 + 0 = mgh + (1)/(2)m(5.23)^2`

divide whole equation by mass "m"

`9.8*2.75 = 9.8*h + (1)/(2)*27.35`

`9.8*h = 13.27`

`h = 1.35 m`

so height of the ball from ground will be 1.35 m