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# Edexcel AS Mechanics 1 revise doubt watch

1. Hi, I worked out a question in the revision guide of edexcel AS mechanics and I got the answer 50 but in the answers it says that it is 42 not 50. I have no idea how that answer could be worked out. Please help me. This is the question:

A car is travelling along a straight motorway at a constant speed V m/s. Ten seconds after passing a speed-limit sign, the driver brakes and the car decelerates uniformly for 5 seconds, reducing its speed to 30m/s. Given that the car covers a distance of 600m in the 15 second period, find the value of V.

2. Show me your working out

It helps to sketch a velocity-time graph where the area under the graph is the displacement covered.
3. (Original post by ManLike007)

It helps to sketch a velocity-time graph where the area under the graph is the displacement covered.
I drew a velocity-time graph and calculated the area.
600=1/2 * (V-30) * 15 + 30*15
4. (Original post by Rashina)
I drew a velocity-time graph and calculated the area.
600=1/2 * (V-30) * 15 + 30*15
Your calculation of the area of a trapezium looks wrong

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5. (Original post by gdunne42)
Your calculation of the area of a trapezium looks wrong

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Thank you.Now I got it correct. I got the answer.

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