Question

A pile driver weighing 1500 pounds drops with the speed of 20 ft/sec. What is the kinetic energy of the pile driver when it hits a steel beam that it is driving into the ground?

Answer 1

`KE ~= 13 kJ`

Explanation:

This requires changing the data into SI units. (Sorry, I can't deal with mass in slugs - or kinetic energy in anything other than Joules.)

`1500 cancel(pounds) * (1 kg)/(2.2 cancel(pounds)) = 689 kg`

`20 cancel(ft)/(sec) * (0.305 m)/(1 cancel(ft)) = 6.1 m/s`

`KE = 1/2*m*v^2 = 1/2*689 kg*(6.1 m/s)^2`

`KE = 12,819 J ~= 13 kJ` (2 significant digits)

I hope this helps,
Steve