# If an object with a mass of #2 kg # changes speed from #9m/s# to #4 m/s#, by how much does its kinetic energy change?

##### 1 Answer

Feb 18, 2016

#### Explanation:

The formula for kinetic energy is given by

#"KE" = 1/2 m v^2#

Initially, the kinetic energy is

#"KE"_"i" = 1/2 (2 "kg")(9 "m/s")^2#

#= 81 "J"#

In the end, the kinetic energy is

#"KE"_"f" = 1/2 (2 "kg")(4 "m/s")^2#

#= 16 "J"#

The change in kinetic energy is given by

#Delta "KE" = "KE"_"f" - # #"KE"_i#

#= 16 "J" - 81 "J"#

#= -65 "J"#