Maximizing Cyclist Speed: Solving the Energy Question in a Race

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In summary, a cyclist with an initial speed of 21 km/h and 3.0 * 10^2 W of power is able to convert 92% of input energy into kinetic energy. After 4 seconds, the cyclist will be traveling at a speed of 7.9 m/s. The combined mass of the cyclist and the bicycle is 78 kg. This is found by calculating the useful energy given and using it to determine the change in kinetic energy and final velocity. The final speed is 11.15 m/s.
  • #1
neededthings
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A cyclist is competing in a race and decides to pass some fellow cyclists who are getting tired. The initial speed of the cyclist is 21 km/h and he has 3.0 * 10^2 W of power. If the bicycle is able to convert 92% of input energy into kinetic energy, how fast will cyclist be traveling after 4.0 s. The combined mass of the cyclist and the bicycle is 78 kg.

The answer is 7.9 m/s. But I don't know how.
 
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  • #2
show us your attempt... then we will help you...!
 
  • #3
energy= Pt= 3x10^2 * 4 = 1.2 x10^3 J
Useful energy = 1.2 x10^3 *0.92 = 1.104 x10^3
KE= 1/2m( v)^2
root(1.104 x10^3 *2 /78) = change in v = +/-5.32 m/s (3 S.F.). He is accelerating hence +5.32m/s
21km/h = 21000m/60x60s= 5.83 m/s (3 S.F)
Total speed = 5.32+5.83 = 11.15m/s
 
  • #4
useful energy =1.104x10^3 ... right
then change in kinetic energy will be equal to useful energy given in 4 seconds...
the formula 1/2mv^2, 'V' is the instataneous velocity, not the change in velocity
so we get
change in kinetic energy = useful energy given..
mx(Vfinal2-Vinitial2)/2
 
  • #5
I don't understand your solution. Can you please Clarify
 
  • #6
neededthings said:
energy= Pt= 3x10^2 * 4 = 1.2 x10^3 J
Useful energy = 1.2 x10^3 *0.92 = 1.104 x10^3
KE= 1/2m( v)^2
root(1.104 x10^3 *2 /78) = change in v = +/-5.32 m/s (3 S.F.). He is accelerating hence +5.32m/s
21km/h = 21000m/60x60s= 5.83 m/s (3 S.F)
Total speed = 5.32+5.83 = 11.15m/s

Whoa, back it up a bit. You've got the energy input correct. What's your initial kinetic energy? Add the energy input to that to get the final kinetic energy. Use that to get a final velocity.
 
  • #7
Kishlay said:
useful energy =1.104x10^3 ... right
then change in kinetic energy will be equal to useful energy given in 4 seconds...
the formula 1/2mv^2, 'V' is the instataneous velocity, not the change in velocity
so we get
change in kinetic energy = useful energy given..
mx(Vfinal2-Vinitial2)/2

initial kinetic energy + useful energy given= final kinetic energy
 
  • #8
hope this will make you clear
 
  • #9
I get 21 which is not the correct? Please Help
 
  • #10
never mind i got it.

Thanks alot
 
  • #11
he he he ...
if you have really got it then it is fine, if not we are always to help you...!
 

1. What is "Energy Question Problem"?

"Energy Question Problem" refers to the various issues and challenges related to the production, distribution, and consumption of energy. It encompasses topics such as renewable energy, energy efficiency, and the impact of energy use on the environment.

2. What are the main sources of energy?

The main sources of energy are fossil fuels (such as coal, oil, and natural gas), nuclear energy, and renewable sources (such as solar, wind, hydro, and geothermal energy). Each source has its own advantages and disadvantages, and the choice of energy source often depends on factors such as cost, availability, and environmental impact.

3. How does energy production affect the environment?

Energy production can have various impacts on the environment, depending on the source of energy. Fossil fuels, for example, emit greenhouse gases and contribute to air pollution, while renewable sources have a much lower impact. The extraction and transportation of energy sources can also have negative effects on the environment and local communities.

4. What are some solutions to the energy question problem?

There are various solutions to the energy question problem, including increasing energy efficiency, transitioning to renewable energy sources, and promoting sustainable lifestyles. Government policies, technological advancements, and individual actions all play a role in addressing this issue.

5. How can individuals contribute to solving the energy question problem?

Individuals can contribute to solving the energy question problem by making small changes in their daily lives, such as conserving energy at home, using public transportation or alternative modes of transportation, and supporting renewable energy initiatives. Educating oneself and others about the importance of sustainable energy practices and advocating for policy changes can also make a difference.

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