4 (a) Two cyclists ride on a hilly road and go through points P, Q, R and S - Edexcel - GCSE Physics Combined Science - Question 4 - 2021 - Paper 1
Question 4
4 (a) Two cyclists ride on a hilly road and go through points P, Q, R and S.
The diagram in Figure 7 shows how the vertical height of the road changes during
the jou... show full transcript
Worked Solution & Example Answer:4 (a) Two cyclists ride on a hilly road and go through points P, Q, R and S - Edexcel - GCSE Physics Combined Science - Question 4 - 2021 - Paper 1
Step 1
The greatest overall change in gravitational potential energy for each cyclist is between which two points on the journey?
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Answer
The correct answer is D R and S. This is because the difference in vertical positions between R and S is greater than any other pair of points on the journey.
Step 2
Calculate the total amount of work done against gravity when the cyclist travels from point P to Q.
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Answer
To calculate work done, we use the formula:
workextdone=force×distance
Given that the cyclist's weight (force) is 700 N and the vertical distance (height) from P to Q is 20 m:
workextdone=700×20=14000 J
Step 3
Calculate the mass of this cyclist.
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Answer
Using the equation for gravitational potential energy change:
ΔGPE=m×g×Δh
Where:
( \Delta GPE = 11,250 \text{ J} )
( g = 10 \text{ N/kg} )
( \Delta h ) can be derived from the height difference Q to R (giving 20 m).
Rearranging for mass:
m=g×ΔhΔGPE=10×2011250=56.25 kg
Step 4
Explain why the total amount of work done by a cyclist between points Q and R is different from the change in gravitational potential energy of the cyclist between points Q and R.
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Answer
The total work done by a cyclist on a journey includes not only the work done against gravity but also the work done against other forces like friction and air resistance. Therefore, even if the change in gravitational potential energy is significant, the actual work done will also account for energy lost to these other forces.
Step 5
Lubricating the chains and wheel bearings helps to
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Answer
The correct answer is C increase the efficiency of the cyclist and bicycle. Lubrication reduces friction between moving parts, allowing for a more efficient transfer of energy, rather than decreasing efficiency.
Step 6
Calculate the velocity of this cyclist.
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Answer
Using the formula for kinetic energy:
KE=21mv2
Given that the kinetic energy (KE) is 2800 J and the mass (m) is 85 kg, we can rearrange the equation to solve for velocity (v):
