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

2 Answers
Apr 15, 2018

Answer:

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

Apr 15, 2018

Answer:

#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"#