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So i was given this question:

• If two people are on a train that is travelling at 200km/hr westward along the equator and they decide to play catch. The person throwing the ball is at the back of the train car and the person catching the ball is at the front of the train car. The ball is thrown at 125km/hr.

•   The Earth rotates once in about 24 hours with respect to the sun and once every 23 hours 56 minutes and 4 seconds with respect to the stars

•   The circumference of the earth at the equator is 40,075km

•   The earth travels at 30km/sec around the sun

•   Assume the sun is stationary

Relative to the telephone pole the train just past, how fast is the ball travelling?

I feel like this is a trick question with all the extra information given.

I just assumed that the ball is thrown 125km/hr in a train that is going 200km/hr so i assumed you simply add both speeds so 125+200 = 325km/hr and that is the answer.

Is this correct?

Darrick
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  • Just a remark: I wonder why the equator is not exactly of length 40000km (that's a definition of the meter). – anderstood Oct 08 '16 at 02:45

1 Answers1

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Yes, you are correct.

In the sense of every movement is related to at least two objects, and in this case they are the ball and the telephone pole. Since the telephone pole is also on the surface of the Earth so you can actually ignore the informations given which are not affecting the relationship between the ball and the telephone pole. Therefore just consider the speed of the train and the speed of the ball traveling in the air.

Answer: 200+125 = 325 km/hr

However, it's not exactly 325km/hr

The thing is, the surface of the Earth is curved, so the straight distance between the telephone pole and the ball is slightly shorter than the surface distance. However the error is just too small so you can ignore that too.

Maxwell Li
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