Question

What is the kinetic energy of an object with a mass of `5 kg` that has been in freefall for `2 s`?

Answer 1

960.4 J

Explanation:

The formula of Kinetic energy is `1/2mv^2` where m is mass and v is velocity. This simply means that a mass m moving with a velocity v has kinetic energy `1/2mv^2`.

We know mass, so lets find velocity. It is given that it has been falling for two seconds. So its velocity `= a times t` .In this case the acceleration is caused due to gravity and hence acceleration is 9.8 meters per second squared.

Plugging it into the equation, if it has been falling for 2 seconds, then its velocity is `9.8 times 2 = 19.6` meters per second

Now since we have velocity, we can find Kinetic energy by simply putting the values of mass and velocity in the first equation

K.E.=`1/2 times 5 times 19.6^2`= 960.4 J

Answer 2

`960.4` joules

Explanation:

Well, kinetic energy is defined through the equation,

`"KE"=1/2mv^2`

• `m` is the mass of the object in kilograms

• `v` is the velocity of the object in meters per second

The velocity of the free-fall object is defined through the equation,

`v=u+at`

• `u` is the initial velocity

• `a` is the acceleration of the object

• `t` is the time in seconds

In this case, `a=g=9.8 \ "m/s"^2`, assuming air resistance is negligible.

If the object was dropped from something, then `u=0`, and so:

`v=0+9.8 \ "m/s"^2*2 \ "s"`

`=19.6 \ "m/s"`

Therefore, the kinetic energy is:

`"KE"=1/2*5 \ "kg"*(19.6 \ "m/s")^2`

`=2.5 \ "kg"*384.16 \ "m"^2"/s"^2`

`=960.4 \ "kg m"^2"/s"^2`

`=960.4 \ "J"`