A couple of questions

[medtrack]

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Hello,

I have some questions that I am struggling with. Forgive my grammar, I wrote them as I was working through problems


1) Car accident against brick wall. Drivers leg gets compressive stress that results in fracture. What would most likely prevent such a fracture.
Formulas for Youngs Modulues E=(F/A)/deltaL/L

Would think decrease by mass by two as an answer but answer is a decrease in his velocity by two (since velocity is squared). Seems intuitive but there is no velocity in the formula.

2) H2O(l) + CO2(g) → H2CO3(aq) + H+(aq) + HCO3–(aq)

why is the aqueous solution made weakly acidic and not strongly acidic?

3) mirror, which is made of glass of refractive index 4, were repositioned so that the laser beam strikes at an angle of 60° to its surface, what would be the angle of reflection?

Why 30 if not specified to normal. Are we always giving answer in respect to normal for these q’s

4) ramp with angle (x). why is static frictional force umgcosx and not umgsinx, since sin is parallel to ramp and static friction should be parallalel to movement (hence the ramp).?

5) When we decrease an angle of an incline the frictional force increases since its dependent on cos. Intuitively how does this make sense? Wouldn’t we need more friction as we raised incline to keep object from moving?

6)why is the second ionization energy higher than the first? For example if we take one electron from calcium it is in +1, but then taking a second one away (+2) would make it more stable as a full octet. Why would it take more energy to get rid of an electron that would leave calcium in a better electronic configuration?

 

[Heday]

1) Car accident against brick wall. Drivers leg gets compressive stress that results in fracture. What would most likely prevent such a fracture.
Formulas for Youngs Modulues E=(F/A)/deltaL/L

Would think decrease by mass by two as an answer but answer is a decrease in his velocity by two (since velocity is squared). Seems intuitive but there is no velocity in the formula.

Similar question has been posted: http://forums.studentdoctor.net/showthread.php?t=1023053

2) H2O(l) + CO2(g) → H2CO3(aq) + H+(aq) + HCO3–(aq)

why is the aqueous solution made weakly acidic and not strongly acidic?

Basically you're taking H2O & CO2 and making carbonic acid (H2CO3), right? There are six strong acids you need to commit to memory: HCl, HBr, HI (notice how these three are from the halogens), Nitric acid (HNO3), Perchloric acid (HClO4), and Sulfuric acid (H2SO4). All other acids are "weak acids." Basic gen chem knowledge.

3) mirror, which is made of glass of refractive index 4, were repositioned so that the laser beam strikes at an angle of 60° to its surface, what would be the angle of reflection?

Why 30 if not specified to normal. Are we always giving answer in respect to normal for these q’s

Angle of reflection = angle of incidence.

4) ramp with angle (x). why is static frictional force umgcosx and not umgsinx, since sin is parallel to ramp and static friction should be parallalel to movement (hence the ramp).?

static friction (and kinetic for that matter) = u*N
N = normal force, which is equivalent to umgcosx (see picture above).

5) When we decrease an angle of an incline the frictional force increases since its dependent on cos. Intuitively how does this make sense? Wouldn’t we need more friction as we raised incline to keep object from moving?

Yes, we would need more friction as we raised the incline plane to keep the object from moving. However, if we decrease the angle of an incline plane, the object is less likely to slide off the plane. If we were to increase the angle, the object would begin to slide, (and as you increase the angle, the object would fall quicker and quicker). Intuitively... an object is less likely to slide on a flat surface (angle of zero) than say a very steep surface (large angle).

6)why is the second ionization energy higher than the first? For example if we take one electron from calcium it is in +1, but then taking a second one away (+2) would make it more stable as a full octet. Why would it take more energy to get rid of an electron that would leave calcium in a better electronic configuration?

Let's dumb it down to just a smaller atom, let's take Be, it has 4 protons and 5 neutrons, consequently, at a net zero charge, Be would have 4 electrons. Very simple concept (and very useful) is that opposite charges attract. Therefore the protons are attracted to the electrons and vice versa. So what happens when you remove an electron? You're left with 3 electrons and 4 protons. Now these protons are holding the 3 electrons even more tightly because there is less negative charge to go around. Make sense?

Think about atomic radii, they decrease from left to right because you're adding protons which pull the electrons even closer.

 

[medtrack]

Similar question has been posted: http://forums.studentdoctor.net/showthread.php?t=1023053





Yes, we would need more friction as we raised the incline plane to keep the object from moving. However, if we decrease the angle of an incline plane, the object is less likely to slide off the plane. If we were to increase the angle, the object would begin to slide, (and as you increase the angle, the object would fall quicker and quicker). Intuitively... an object is less likely to slide on a flat surface (angle of zero) than say a very steep surface (large angle).



Let's dumb it down to just a smaller atom, let's take Be, it has 4 protons and 5 neutrons, consequently, at a net zero charge, Be would have 4 electrons. Very simple concept (and very useful) is that opposite charges attract. Therefore the protons are attracted to the electrons and vice versa. So what happens when you remove an electron? You're left with 3 electrons and 4 protons. Now these protons are holding the 3 electrons even more tightly because there is less negative charge to go around. Make sense?

Think about atomic radii, they decrease from left to right because you're adding protons which pull the electrons even closer.

The last explanation makes sense.

Going back to the question on frictional forces, the frictional force increases as the angle decreases. However, wouldn't you expect a higher frictional force at a higher angle since a block would have a higher tendency to slide than say a block at 10 degrees?

Thanks!