Question

A car is traveling with a velocity of 30 m/s has a kinetic energy of 800,000 J. What is the mass of the car?

Answer 1

The mass of the car is 1800 kg.

Explanation:

Kinetic energy is the energy of motion. Anything that has motion has kinetic energy.

The equation for determining kinetic energy is `"KE"=1/2mv^2`, where `"KE"` is kinetic energy in J, `m` is mass in kg, and `v` is speed in m/s.

Given
`"KE=800000 J"="800000 kg·m"^2/"s"^2`
`v="30 m/s"`

Unknown
`m`

Solution
Rearrange the equation to isolate `m` and solve.

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

`m=(2"KE")/(v^2)`

`m=(2·800000"kg·m"^2/"s"^2)/((30"m/s")^2"`

`m=(2·800000"kg·m"^2/"s"^2)/(900"m"^2/"s"^2)`

`m="1800kg"` (rounded to two significant figures)

http://academic.umf.maine.edu/magri/PUBLIC.acd/tools/SigFigsAndRounding.html