Calculating the work done on a motorcycle and rider

[member 661905]

Homework Statement

A motorcycle and rider have a combined mass of 350kg.

The wheels each have a mass of 20kg, diameter of 500mm and radius of gyration of 200mm.

The rider accelerates from 5m/s to 25m/s over a distance of 100m, whilst climbing a hill of slope 1 in 20.

The average resistance to motion, including drag, is 120N.

a) Determine the total work done as the motorcycle ascends the incline.

b) Calculate the amount of power developed during the climb.

c) Explain the energy transfer that is taking place within this system.

Relevant Equations

YET TO FIND

IN PROGRESS

 

[willem2]

You should really be able to do a). Where does all the work that the motor does go?
for b) I think you have to assume constant acceleration

 

[member 661905]

You should really be able to do a). Where does all the work that the motor does go?
for b) I think you have to assume constant acceleration

Please have a look if I am right

 

[willem2]

Your calculation of acceleration is correct. The calculation for the force needed to cause this acceleration ignores that you force to get the wheels to rotate as well.
You also add the 120N resistance to the force, and then you subtract it again later.
Your calculation of the force needed to overcome gravity doesn't make it into the final answer.

Finally when you calculate the power, you use P = F.V. You can only use this to calculate the average power if either the force or the speed is constant. If the acceleration is constant, both the force and the speed change.
You also use the energy instead of the force in this calculation, so your answer is much too high.
It's probably easier to use Power = Energy/time for b) since you already calculated the energy in a)

 

[member 661905]

PLEASE IF POSSIBLE CAN YOU PROVIDE ME YOUR SOLUTION TO STUDY
THANKS FOR THE TIME

 

[haruspex]

PLEASE IF POSSIBLE CAN YOU PROVIDE ME YOUR SOLUTION TO STUDY
THANKS FOR THE TIME

That's not how things work on the homework forums.

As willem wrote, you found the acceleration ok, but you do not need that for part a.
Try to find the initial KE (don't forget the rotational energy of the wheels) the final KE, and the work done against gravity and friction.

 

[member 661905]

That's not how things work on the homework forums.

As willem wrote, you found the acceleration ok, but you do not need that for part a.
Try to find the initial KE (don't forget the rotational energy of the wheels) the final KE, and the work done against gravity and friction.

Thanks Willem2 and haruspex , please have a look what i have done on the question .
I solved the continuation of the question too =
At another point in its journey, the motorcycle and rider travel at 80 km/h around a left-hand bend of radius 30m. Calculate:

• The angular velocity of each of the wheels.

• The moment of inertia of each wheel.

• The magnitude and effect of the gyroscopic torque produced on the bike.

 

[LeafNinja]

Thanks Willem2 and haruspex , please have a look what i have done on the question .

First, when you're calculating force, you're ignoring the gravity force. Additionally, you don't really need to calculate forces in this problem.Also, when you use the formula

$W=Fs$​

You're only factoring in translational kinetic energy. In order to final total kinetic energy you need both translational and rotational kinetic energy.

$W_{total}=\Delta T = \Delta T_{rot}+\Delta T_{trans}=\Delta [2*\frac{1}{2}I_{w}(\frac{v}{r})^{2}+\frac{1}{2}mv^{2}]$​

To calculate the work done by the engine, simply add the work needed to overcome gravity and drag.

$W_{engine}=W_{total}+W_{g}+W_{D}$
​

Where $W_{g}=mgs(sin(\theta ))$ and $W_{D}=F_{D}s$

When finding power, you shoud use $P_{av}=\frac{W}{t}$ where $t=\Delta v/a$