- #1
Cici2017
Homework Statement
Homework Equations
The Attempt at a Solution
Can someone tell me what formula to use? Is it p=RA/L? but what about the mass? Thanks~
Resistance of a cylindrical resistor
- Thread starter Cici2017
- Start date
AI Thread Summary
The discussion focuses on understanding the resistance of a cylindrical resistor, emphasizing the importance of grasping the physical concepts rather than solely relying on formulas. The formula p=RA/L is mentioned, but participants suggest that understanding the relationship between mass and volume is crucial, particularly in comparing smaller and larger resistors. Participants advocate for using thought experiments to enhance comprehension of the principles involved. It is highlighted that without a solid understanding of the underlying concepts, using formulas may lead to superficial learning. Overall, a deep physical understanding is deemed essential for effectively applying the relevant equations.
Can someone tell me what formula to use? Is it p=RA/L? but what about the mass? Thanks~
- #2
Dadface
- 2,489
- 105
What can you infer about the volume of the smaller resistors compared to the volume of the larger resistor?
- #3
Cici2017
p=m/V ,Dadface said:
if m half, V half,
V=πr2L
right?
- #4
epenguin
Science Advisor
- 3,637
- 1,013
Cici2017 said:
I will tell you don't use any formula. It will do you no good, maybe less than none. Use physical thinking. Use a thought experiment like slicing a resistor in two.
Get the physical understanding then that will help you understand the formula!
- #5
Dadface
- 2,489
- 105
I agree with epenguin who has given you very good advice. If you do need to refer to a formula try to get a good understanding of what the formula is actually referring to. In many cases you will find it's common sense. Without understanding the formula you're just substituting numbers and probably learning very little.
Neglect gravity other than that of water; neglect friction.
F1=ρgsh=1000*10*1*(1+4)=50000 N;
F1=ρgsh=1000*10*0.1*4=4000 N;
F3=50000-4000=46000 N?
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system
$$M(t) = M_{C} + m(t)$$
$$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$
$$P_i = Mv + u \, dm$$
$$P_f = (M + dm)(v + dv)$$
$$\Delta P = M \, dv + (v - u) \, dm$$
$$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$
$$F = u \frac{dm}{dt} = \rho A u^2$$
from conservation of momentum , the cannon recoils with the same force which it applies.
$$\quad \frac{dm}{dt}...
I was thinking using 2 purple mattress samples, and taping them together, I do want other ideas though, the main guidelines are;
Must have a volume LESS than 1600 cubic centimeters, and CAN'T exceed 25 cm in ANY direction.
Must be LESS than 1 kg.
NO parachutes.
NO glue or Tape can touch the egg.
MUST be able to take egg out in less than 1 minute.
Grade A large eggs will be used.
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