Biomechanics Question: need help!?

[Namus]

Hi all,

 

First time here; I was just looking for help on a couple of Biomechanics questions I have:

 

1. You are moving into your new apartment and you are pushing a bookcase across a carpeted floor. The coefficient of friction between the bookcase and the floor is 0.65. What force is required to move the bookcase if its mass is 40 kg. Assume gravity equals 9.81 m/s².

 

2. In a Nike shoe design laboratory, the frictional properties of a shoe are being tested. The shoe is placed on a piece of board and then one end of the board is raised. The raising of the board from one end creates a slope. The board is continuously raised from one end until the shoe begins to slide down the board. For one shoe, this angle is 35º. Calculate the frictional force, the normal force and the coefficient of friction if the shoe’s mass is 200 grams. Report your answers to 2 decimal places.

 

3. A vertical jump is performed and the only data made available to you is the flight time of the jumper which is 0.600 s. Calculate the jump height achieved. Report your answer to 2 decimal places.

 

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I don't necessarily want the answers; I'd much prefer to understand the process involved in finding the answers so I can do it myself; At this point though, I'm pretty much stumped :S

 

Any assistance with regards to these would be MOST greatly appreciated

 

Thanks again everyone:cool:

 

P.S. I hope I posted this in the right section :S

[savata71]

3. A vertical jump is performed and the only data made available to you is the flight time of the jumper which is 0.600 s. Calculate the jump height achieved. Report your answer to 2 decimal places.

 

The time here is not enough. Mass does't matter but you need a starting (initial) velocity to solve jump height.

I will try to write how it solves after consulting with my books.

Edited April 5, 2009 by savata71

[Namus]

That's the question exactly as it was given to me; there is an answer (not multi-choice) apparently to be given in metres (m)

[savata71]

Ok, maybe the time is enough. Now I am checking it.

[Mokele]

For #1, you should have a formula or example in your book that lines up with this almost exactly. Read up on how to calculate friction.

 

For #2, try doing a free body diagram, and note that gravity will both pull the shoe against the ramp and slide it down, and the relative proportions of those depends upon the incline. Add in what you know about friction from #1.

 

For #3, look up formulats for ballistic motion. Those apply even in vertical cases.

[Mokele]

I deleted it - we're here to provide *help*, not just give people the answers. The OP even specifically stated that they just wanted pointers, not full answers.

[savata71]

ok, i understand

[HiroJ]

ok, for three its simple... 0.6 seconds for jump. 0.3 seconds going upward and 0.3 seconds going down again. acceleration due to gravity is 9.81 m/s. if you multiply m/s * s you will get an answer in metres

[savata71]

For #1 and #2 watch Lec 8 | 8.01 Physics I: Classical Mechanics, Fall 1999:

 

http://www.youtube.com/watch?v=uZGbtK2KBoY

 

and you will do them

 

#3 is much harder for understanding and solving - you have to pass through examples for how similar problems are solved.Because differential equations and integrations are involved.

Edited April 5, 2009 by savata71

[Mokele]

#3 does not require differential equations - you can do it with simple algebra.

[savata71]

Yes, if we use the law of conservation of energy. The potential energy in highest position is equal to kinetic energy in starting position. That way it can be solved without differential equation, indeed.

[Mokele]

You can also solve it via simple kinematics equations, without diff. eq.

[savata71]

You can also solve it via simple kinematics equations, without diff. eq.

 

Yes, of course – I saw it now. It is absolutely simple. And I am trying swim in deep waters…