Answer to Question #266236 in Mechanics | Relativity for JINGJING

Question

Neglecting air resistance, how long shall it take an object in free fall to have a velocity of 5.0 m/s?

Answer 1

Explanations & Calculations

• Since gravitational acceleration is almost constant in low heights where most of the things happen you can use the 4 equations of motion appropriately.
• The question is asking for the travelled distance until it attains the given velocity having given only the gravitational acceleration and the final velocity you can use $\small v^2=u^2+2as$.
• Then,

$\qquad\qquad \begin{aligned} \small h&=\small \frac{v^2-u^2}{2g}\\ &=\small \frac{(5ms^{-2})^2-u^2}{2\times9.8ms^{-2}} \end{aligned}$

• If the object falls from rest (u=0) it falls through a distance $\small h=1.3\,m$
• If it has an initial velocity (u>0) then its velocity needs to be calculated accordingly using that equation.