Question

A cinder block is sitting on a platform 20 m high. It weighs 79 N. How much energy does the block have?

Answer 1

1580 J

Explanation:

First, we need to figure out what kind of energy we are trying to find. As the cinder block is high up in the air and is not moving, it will have potential energy.

The equation for potential energy is
`E_p=mgh`
Where `E_p` is the potential energy
`m` is the mass of the object
`g` is the gravitational acceleration. On Earth, `g` is `9.8 ms^-2`

Then we need to list all the known values:
Weight: `W=79 N`
Height: `h=20 m`

it may look like we are missing the `m` and `g` in the equation
But, we can look at what `W` actually is:
`W=mg`

Hence we can substitute `mg` into the potential energy equation:
`E_p=mgh`
`=>E_p=Wh`

Then we can simpy substitute the values which are given:
`E_p=Wh`
`=>E_p=79N*20m`
`=>E_p=1580 Nm=1580J` (1 Joule is the same as 1 Newton Metre)