wiki:u/johannjc/scratchpad10

Version 1 (modified by Jonathan, 9 years ago) ( diff )

1.) weight density = mass density x g

  • g on Earth is 9.8 m/s2
  • g on Mars is less
  • mass is conserved so it would have the same mass density, however the weight density on the moon would be less

2.) Stress has units of N/m2 = Pa (pascal)

3.) Youngs modulus (E) is the ratio of stress to strain . Strain is dimensionless degree of deformation

We don't know what the length or cross sectional area of each beem is, but we don't need to

This is constant for different forces or deformations

a.)

b.)

4.) Specific weight of gasoline is .7 or so… The unknown substance has a higher specific weight so it will sink in gasoline

5.) Mass is conserved, so if the volume decreases, the density increases

6.) It would be more difficult at sea level because gravity is slightly stronger. The pressure difference needed by your mouth muscles is just where is the length of the straw, and is the local gravitational constant. Atmospheric pressure is also higher at sea level, but the atmosphere is pushing on the fluid in the container as well as the end of the straw - so it doesn't affect the difficulty.

7.)

Bernoulli Equation says that

is constant along the flow

The flow through any section of the pipe is just and if is constant, then so is

If the cross section decreases, the speed must increase to keep the rate of fluid flow constant.

If the speed increases, (and the pipe is horizontal) then the pressure must decrease to keep fixed.

The streamlines also get compressed as the fluid speeds up.

8.) Force = Pressure x Area

First we find the pressure on the piston that is raising the car

Note there is a typo in the problem… It gives the radius in units of cm2 but it should probably be cm (unless they are giving the area and not the radius)

That same pressure will resist the small piston.

So we can calculate the force applied to the small piston

9.) Flow = Area x velocity

a.)

b.)

10.) The gap will become wider. The 'length' of the ring will expand which would narrow the gap, but the radius (and therefore circumference) of the ring will also increase so the net effect will be for the gap to increase.

11.) expansion is just coefficient of expansion times change in temperature

So the 1m rod will become

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