Physics

Question 1

Convert 5.5x10^3 kg/m^3 to g/cm^3

Answer 1

(10^3g / 1 kg) x (1m / 10^2 cm)^3 = 5.5 g/cm^3

-be mindful of converting m^3 into cm^3, in that the ^3 is factored out and then creates a denominator of 10^6 since (10^2)^3 = 10^6

Question 2

Given F=KD^2v^2, where D is diameter, v is speed, and the units for F are kg*m/s^2;
What are the units for K

Answer 2

K = kg/m^3

Be mindful of the algebra when a fraction is squared it means that both numerator and denominator are squared.

kgm/s^2 = K (m^2 * m^2)/s^2

Question 3

What is the slope of a position vs. time graph?

Answer 3

velocity

Question 4

Does the force of pressure in a fluid depend on the direction of the force? Is pressure a vector or a scalar in this instance?

Answer 4

For the MCAT, no, at any given point in a fluid the pressure is the same in all directions, which means that the force does not depend on the orientation of the force.
This would make force a scalar since we are not considering direction of force.

Question 5

What is the unit of pressure?

Answer 5

N/m^2 the “pascal” (Pa)

Question 6

What is 1KPa?

Answer 6

1000 Pa

Question 7

What is normal atmospheric pressure at sea level in kPa?

Answer 7

100 kPa

Question 8

How would I measure the pressure on an object submerged in a tank with a lid on top?

Answer 8

Hydrostatic Gauage pressure: P = pgD
p = density of fluid in the tank
g = acceleration due to gravity
D= depth of the object

Question 9

If there in no lid on a tank, how do you measure the pressure experienced by an object at a certain depth?

Answer 9

Ptotal = Patm + Pgauge

Question 10

Define buoyant force?

Answer 10

Fbouy = (density of the fluid)(Volume of the object submerged in the fluid)(g)

F = pVg

Question 11

What is the density of Water?

Answer 11

1000 kg/m^3

or

1x10^3 kg/m^3

Question 12

What would be the apparent weight of an object completely submerged in a liquid?

Answer 12

Fa = Fg - Fb
or
wa = w - Fb

F apparent = F due to gravity - F buoyancy
or
w apparent = w - F buoy

Question 13

An object weighs 50N, but only 30N when submerged in a liquid who’s specific gravity is 0.8. What is the “objects” specific gravity?

Answer 13

since specifc gravity is simply a ratio of densities of an object to water [p(obj)/p(h2o)] = S.G.
and:
w(obj) = p(obj) x V(obj) x g
and
F(buoy) = p(liq) x V(obj) x g
then
w(obj) / F(buoy) = [( p(obj)V(obj)g  / p(liq)V(obj)g )] = p(obj)/p(liq)
plug in: w(obj) / F(buoy) = 50N/20N
set it eual to: p(obj)/p(liq) = 5/2

If the objects density is 5/2 times the fluids density, then the object’s specific gravity is 5/2 times the fluid’s specific gravity.
S.G.(obj) = (5/2) x (S.G.(liq)) = (5/2)x(0.8) = 2
So the specific gravity of the object is 2, which also translates as the object has twice the density of water.

Question 14

Define Pascal’s Law?

Answer 14

A confined fluid will transmit an externally applied pressure change to all parts of the fluid and the walls of the container without loss of magnitude. Hydraulics: F1/A1 = F2/A2
or Pressure1 = Pressure2 since pressure is Force over Area.

Question 15

What does Pascal’s law also tell us about the relationship of volume between two connected pistons?

Answer 15

Since Pressure1=Pressure2
F1/A1 = F2/A2
and volume = cross sectional area x distance (or depth)
If I push piston 1, with its cross sectional area to a certain depth (A1•d1), then piston 2 will rise its cross sectional area times a certain depth (A2•d2).
So we can say: that A1•d1 = A2•d2
cool
Even cooler, since A•d = m^2 • m = m^3 = Volume
then:
V1 = V2

Question 16

How is the strength of liquid surface tension determined?

Answer 16

The coefficient of surface tension, γ
γ = force per unit length
or N/m = Kgm/s^2 = Kg/s^2

Question 17

What is the surface tension coefficient of water?

Answer 17

γ of water = 0.07 N/m

Question 18

Does the surface nsion coefficient of water increase or decrease when the temperature rises?

Answer 18

γ(water) will decrease as the temperature increases.

Question 19

How would you find the flow rate of fluid moving through a pipe?

Answer 19

Simply multiply the cross-sectional area of the pipe at any point, A, by the average speed of the flow, v, at that specific point.

ƒ=Av

Question 20

What are the SI units for Flow Rate?

Answer 20

ƒ=Av
ƒ=m^2•m/s
ƒ=m^3/s

translated as volume per unit time.

Question 21

What is Flow Speed?

Answer 21

flow speed, do not confuse with flow rate, is simply the velocity of the liquid.

(flow rate describes “how much” per unit time)
(flow speed describes “how fast” is it moving)

Question 22

What is the continuity equation?

Answer 22

Describes how the flow speed of a fluid will change at the cross sectional area of the tube changes. As a tube narrows, the flow speed will increase:

A1V1 = A2V2
or
m^3/s= m^3/s