Question

if michael jordan has a vertical leap of $1.29m$, then what is his hang time (total time to move upwards to the peak and then return to the ground)?
(A) $2.03s$
(B) $1.03s$
(C) $0.03s$
(D) $1.0s$

Answer 1

Hint In these kinds of situations the first thing important is to notice the given problem statement. Specially this is a question regarding some manipulation. First we just have to sort what we got and then we have to find the remaining quantities for the required equation. In this question we will get the answer simply by putting the values in Newton's equations of motion.

Complete step by step answer:
Here, first we have to sort out the given quantities:
Acceleration: $a = - g = - 9.8m{s^{ - 2}}$ , here the negative sign is due to the accelerative nature of the motion.
Velocity: $v = 0m/s$
Vertical distance travelled: $s = 1.29m$
Now, we just have to put the values in the equation of the motion and we wil get the answer:
$
  {v^2} - {u^2} = 2as \\
  {0^2} - {u^2} = 2( - 9.8)(1.29) \\
  u = 5.03m/s \\
 $
If $t$ is the time till it will reach the peak of the motion, so
$
  v = u + at \\
  0 = 5.03 - (9.8)t \\
  t = \dfrac{{5.03}}{{9.8}} = 0.513s \\
 $
Therefore the total time will be:
$
  {t_{total}} = 2t \\
  {t_{total}} = 2 \times 0.513 \\
  {t_{total}} = 1.03s \\
 $

Note Most important thing here is to notice the given values, then we can easily derive the missing quantities . Apart from that it is necessary to observe what process is straight and easy to find the rest values and then we can execute the formulas. In these types of questions interpreting the correct formula to be used is necessary unless it will get twisted.