What is the kinetic energy of an object with a mass of #3 kg# that has been in freefall for # 7 s#?

1 Answer
Feb 26, 2017

Answer:

7kJ of energy

Explanation:

The acceleration on the object is g, or 9.8m/s (assuming no air resistance) This number is a constant that applies to all objects close to the Earth.

Use the equation:

#v_f = v_i + at# (The final velocity is the initial velocity plus the acceleration times time)

In this case, the initial velocity is zero (The object is dropped, not thrown downward) So:

#v_f = at#

#v_f = "gt"#

#v_f = 9.8(m/s^2)*7s#

#v_f = 68.6m/s#

Now for kinetic energy = #(1/2mv^2)#

#KE = 1/2 * 3"kg" * (68.6(m/s))^2#

Which is about #7059# or #7000kJ#