Question

Michael Jordan has a vertical leap of 1.25 m, what is his takeoff speed and for how much time he will be in the air? Take $g=10m{s}^{-2}$.

• A. u = 10 m/s, t = 1 s
• B. u = 5 m/s, t =0.5 s
• C. u = 15 m/s, t = 1.5 s
• D. u = 10 m/s, t = 0.5 s

Answer 1

The correct option is (B) u = 5 m/s, t =0.5 s

Step 1, Given data

Distance =1.25 m

Acceleration due to gravity = $g=10m{s}^{-2}$.

Step 2, Finding initial velocity and time

Let the initial velocity be $u$

According to the question final velocity, $v=0,$ acceleration, $a=-10m{s}^{-2}$ and $s=1.25$ m

From third equation of motion, $v^2=u^2+2as$

$\Rightarrow 0=u^2-2\times 10\times 1.25$

On solving, $u=5m{s}^{-1}$

Now, from first equation of motion, $v=u+at$

$0=5-10\times t$

$\Rightarrow t=\frac{5}{10}=0.5$ s

Hence the initial speed is 5 m/s and time is 0.5 s