Question

An object is falling from a height of 7.5 meters. At what height will its velocity be 7 meters/second?
a. 49 meters
b. 7.5 meters
c. 7.0 meters
d. 5.0 meters
e. 2.5 meters

Answer 1

Data Given
h = 7.5 m, v = 7 m/s and g = 9.81 m/s
From third equation of motion we know that
\[v^{2} - u^{2} = 2as\]

Answer 2

\[7^{2}- 0^{2} = 2\times9.81\times h_{1}\]
\[h_{1} = \frac{ (7)^{2} }{ 2\times9.81 } = 2.5 m\]
Height at which velocity is 7 m/s is
\[h' = h-h_{1} = 7.5 m - 2.5 m = 5.0 m\]
So Option D is correct.