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# Mechanics watch

1. Hi, just stuck on this question, if someone could help that would be great. Not really sure how to work it out and what the answer is.

"A train travels 14 km in 16 minutes, starting and finishing at rest. The acceleration is half the deceleration, both being uniform, and there is a period during which the train travels at a constant speed of 75 km/hour. Determine how long the period is."
2. (Original post by bobv567)
Hi, just stuck on this question, if someone could help that would be great. Not really sure how to work it out and what the answer is.

"A train travels 14 km in 16 minutes, starting and finishing at rest. The acceleration is half the deceleration, both being uniform, and there is a period during which the train travels at a constant speed of 75 km/hour. Determine how long the period is."
Convert to base units would be a start. From there, work out the average speed for the whole period; and see what you can do with that.
3. Thank you, I know how to change km to m, and minutes to seconds, but do I need to change km/hour to ms^-1 because I'm not sure how to do that?
4. (Original post by bobv567)
Thank you, I know how to change km to m, and minutes to seconds, but do I need to change km/hour to ms^-1 because I'm not sure how to do that?
If you have your speed as km/hour then you could either first change it to m/hour and then into m/s by multiplying it by 1000 and then divide it by 3600 (since one hour is 3600 seconds), or because you know that you will have to multiply it by 1000 and then divide it by 3600, you could directly multiply your speed by 10/36 or 1/3.6.

Edit: Or since you have the distance in km, you could just change the speed to km/s by dividing it by 3600. This should also give you the same time.

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