A cyclist is travelling along a straight, flat road at a constant velocity of 12 m/s. The cyclist then brakes uniformly and comes to rest in 6 seconds. Explain what the velocity–time graph for the entire journey described would look like, and describe the motion of the cyclist during each phase.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A cyclist travels at a constant velocity before applying the brakes and stopping.
Model answer (5 marks)
The graph consists of two straight‑line sections. From t=0 to t≈2.0 s the line is horizontal at 12 m s⁻¹, showing the cyclist moves with constant velocity. From t≈2.0 s to t=8.0 s the line slopes downwards to 0 m s⁻¹, a straight line with a negative gradient, indicating a constant (uniform) deceleration. The slope equals –2 m s⁻² (12 m s⁻¹ ÷ 6 s). During the first phase the net force on the cyclist is zero; during the second phase a constant braking force produces the uniform deceleration until the cyclist stops at t=8 s.
Examiner tips
- Show the two straight‑line sections and label the horizontal part at 12 m s⁻¹; give the slope of the braking section as –2 m s⁻².
- Explain the forces: zero during constant speed, constant braking force during deceleration.
- Mention that the graph ends at zero velocity after 6 s of braking.
Mark scheme (5 marks)
- The first section of the graph is a horizontal straight line (at 12 m/s), indicating constant velocity.
- During the constant velocity phase, acceleration is zero (resultant force is zero).
- The second section of the graph is a straight line with a negative gradient (sloping downward from 12 m/s to 0 m/s).
- The straight negative gradient indicates uniform / constant deceleration (deceleration is uniform because the gradient is constant).
- The graph ends at zero velocity after 6 seconds of braking, showing the cyclist has come to rest / stopped.
Key terms in this question
constant velocity · velocity–time graph
Related
- All Edexcel A-Level Physics (9PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Motion questions
- A skateboarder starts from rest at the top of a slope. She rolls down the slope,…
- A sprinter starts from rest and accelerates along a straight track. After 4 seco…
- A delivery van travels along a straight road at 20 m/s. The driver sees an obsta…
- A car travels along a straight road. It starts from rest and accelerates uniform…