What is the kinetic energy of an object with a mass of 1 kg that has been in freefall for 4 s?

Apr 6, 2018

$\approx 800 J$

Explanation:

Given that it has been falling free for 4 seconds from rest we can use the equation:

$v = u + a t$
$a = 9.81 m {s}^{-} 2$
$u = 0$
$t = 4 s$

Hence
$v = 39.24 m {s}^{-} 1$

Now using the kinetic energy equation:

${E}_{k} = \left(\frac{1}{2}\right) m {v}^{2}$
${E}_{k} = \left(0.5\right) \times 1 \times {\left(39.24\right)}^{2}$
${E}_{k} = 769.8 \approx 800 J$ as we only had 1 significant figure in the question we should answer to 1 significant figure.