A cyclist is riding a bicycle at a steady velocity of 12 m/s. The cyclist and bicycle have a total mass of 68 kg. (a) Calculate the kinetic energy of the cyclist and bicycle. Use the equation $$KE = \frac{1}{2} \times m \times v^2$$ kinetic energy = _____________ J (b) Describe the energy transfer that happens when the cyclist uses the brakes to stop. (d) An athlete uses a training machine in a gym. The display on the machine shows the time spent on the machine and the amount of energy transferred during a training session. Figure 3 shows the displays for two different sessions by the same athlete. Energy 45.2 kJ Energy 37.9 kJ Time 300 s Time 300 s Explain what the displays show about the average power of the athlete in each of these two sessions.

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A cyclist is riding a bicycle at a steady velocity of 12 m/s - Edexcel - GCSE Physics: Combined Science - Question 2 - 2018 - Paper 1

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A cyclist is riding a bicycle at a steady velocity of 12 m/s. The cyclist and bicycle have a total mass of 68 kg. (a) Calculate the kinetic energy of the cyclist a... show full transcript

Worked Solution & Example Answer:A cyclist is riding a bicycle at a steady velocity of 12 m/s - Edexcel - GCSE Physics: Combined Science - Question 2 - 2018 - Paper 1

Step 1

Calculate the kinetic energy of the cyclist and bicycle.

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Answer

To calculate the kinetic energy (KE) of the cyclist and bicycle, we can use the equation:

$KE = \frac{1}{2} \times m \times v^2$

Substituting the values:

Mass (m) = 68 kg
Velocity (v) = 12 m/s

The equation becomes:

$KE = \frac{1}{2} \times 68 \times (12)^2$

Calculating this:

$KE = \frac{1}{2} \times 68 \times 144 = 4900 J$

Therefore, the kinetic energy is 4900 J.

Step 2

Describe the energy transfer that happens when the cyclist uses the brakes to stop.

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Answer

When the cyclist uses the brakes to stop, the kinetic energy stored in the cyclist and bicycle decreases. This energy is transferred into thermal energy, predominantly as heat, which is generated through friction between the brake pads and the wheels. As the brakes heat up, the surrounding environment also absorbs some of this energy, causing an increase in thermal energy in the brakes and their surroundings.

Step 3

Explain what the displays show about the average power of the athlete in each of these two sessions.

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Answer

To calculate the average power for each session, we can use the formula:

$Power = \frac{Work}{Time}$

For session 1:

Energy: 45.2 kJ = 45200 J
Time: 300 s

Average Power in session 1: $P_1 = \frac{45200 J}{300 s} = 150.67 W$

For session 2:

Energy: 37.9 kJ = 37900 J
Time: 300 s

Average Power in session 2: $P_2 = \frac{37900 J}{300 s} = 126.33 W$

Therefore, the displays indicate that the athlete generated more power during session 1 compared to session 2.

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