# Math Help - Energy

1. ## Energy

A man on a motorcycle starts from rest from a point A at the bottom of one hill and travels to a point B at the bottom of another hill. The total distance of the journey is 120 km. The resistance to motion is constant at 300 N throughout the journey. Point A is 1500m higher than point B.

The total mass of the man and his motorcycle is 240kg. When the motorcyclist reaches the point B, his speed is 90 km/h. Calculate the work done by the motorcycle during the journey.

OK basically my tutor has left me with this equation.

Total energy at (t=t) = Total energy at t=0

$mgh + \frac{1}{2}mv^2 = mgh + \frac{1}{2}mv^2$

ok when t=0

v=0

m=240000

h= I dont know what h is!!!! is this 1500??

When t=t

v = 90 km/h (does this need changing to mph?)

m = 240000

h = 0?????

I also know the equation work = force*distance

2. your tutor left you with Energy Equation:

$mgh_1 + \frac{1}{2}mv_1^2 = mgh_2 + \frac{1}{2}mv_2^2$

hope you notice that in this problem:

1) the mass is constant

$i.e. mass (m) = 240kg$

{ there is no need to change this to grams (it will only complicate if you do so), so leave it in kg...see #4 }

2) you can also assume that gravity (g) is constant

$i.e. g = 9.8 m/s^2$

3) Point A is 1500m higher than point B.

$i.e. Distance A - Distance B = 1500 m$

For your convenience assume B is ground level. So, $h2$ would be 0 and $h1$ would be 1500 m as you guessed

4)) The resistance to motion is constant at 300 N

since, $1 N = 1 kgm/s^2$

let us keep everything consistent to that unit.

i.e. keep mass in kg, distance in m, and time in seconds.

keeping that in mind, you should change velocity to $m/s^2$

edit: i think you should visit http://www.physicshelpforum.com/physics-help/ for further help. Afterall, it is a physics problem.