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Define (i) velocity and (ii) friction - Leaving Cert Physics - Question a - 2017
Question a
Define (i) velocity and (ii) friction. A car started from rest and accelerated at 0.4 m s² to reach a top speed of 28 m s⁻¹; it maintained this speed for 200 second... show full transcript
Worked Solution & Example Answer:Define (i) velocity and (ii) friction - Leaving Cert Physics - Question a - 2017
Step 1
Step 2
Step 3
(iii) Draw a diagram indicating the main forces acting on the car when it was accelerating.
Answer
In the diagram, the following forces should be indicated:
- Weight (W) acting downwards
- Reaction force (R) from the ground acting upwards
- Driving force from the engine (F_engine) acting forwards
- Frictional force (F_friction) acting backwards. The driving force should exceed the friction for the car to accelerate.
Step 4
(iv) Calculate how long it took the car to reach its top speed.
Answer
To find the time taken to reach the top speed, we can use the formula for acceleration:
\frac{28 \, ext{m/s} - 0 \, ext{m/s}}{t} = 0.4 \, ext{m/s}^2\ \Rightarrow t = \frac{28 \, ext{m/s}}{0.4 \, ext{m/s}^2} = 70 \, ext{s}$$ Thus, it took the car 70 seconds to reach its top speed.Step 5
(v) Sketch the velocity-time graph for the journey.
Answer
The velocity-time graph would show:
- A linear increase in velocity from 0 to 28 m/s over 70 seconds (acceleration).
- A horizontal line from 70 seconds to 270 seconds (constant speed).
- A linear decrease from 28 m/s to 0 over the final 30 seconds (deceleration). The graph should reflect these three phases clearly.