# Kinematics, Newton's Laws, Fun With Engineers

by tri5
Tags: engineers, kinematics, laws, newton
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You are not moving at a constant acceleration the whole distance to shore. The acceleration is only constant while you are throwing the boot. After that your velocity is constant.
 P: 11 Well I tried what you said doing constant velocity but the automated homework system says the answer is still wrong. Attached Thumbnails
 P: 26 Kinematics, Newton's Laws, Fun With Engineers Have you tried using momentum and impulse?
 P: 11 In class we have only covered 1d, 2d kinematics, and Newton's laws. I know momentum is just a restatement of Newtons's 2nd law, but it has not been covered in class yet. The professor insists that this problem can be solved correctly using what was taught in class so far.
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 Quote by tri5 Well I tried what you said doing constant velocity but the automated homework system says the answer is still wrong.
You will cover some distance on the ice between the time that you start the throw and the time you let go of the boot. You did not account for this in your answer.

In other words, you shouldn't be using 29.4 meters the way you did in your work.
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P: 25,228
 Quote by tri5 Well I tried what you said doing constant velocity but the automated homework system says the answer is still wrong.
Now you are taking the whole distance travelled at a constant velocity. That's not right either. He travels part of the way while accelerating and part of it at constant velocity. It's not really clear to me that they mean you to subtract the mass of the boot either.
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 Quote by Dick It's not really clear to me that they mean you to subtract the mass of the boot either.
I agree. That "Take your weight to be 545.0 N." is a bit ambiguous. However, the parenthetical remark "(Lucky for you that, as an engineer, you sleep with your knife in your pocket and your boots on)" suggests that that 545.0 newtons includes the knife and the boots.

Aside: This is a *bad* question. I calculate that the engineer's throwing arm has to be over 90 meters long.