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Alika [10]
2 years ago
14

You're a safety engineer reviewing plans for a university's new high-rise dorm. The elevator motors draw 20 A and behave electri

cally like 2.6-H inductors. You're concerned about dangerous voltages developing across the switch when a motor is turned off, and you recommend that a resistor be wired in parallel with each motor.
1) What should be the resistance in order to limit the emf to 70 V?
2) How much energy will the resistor dissipate?
Physics
1 answer:
Leya [2.2K]2 years ago
3 0

Answer:

a) R `= 3.5 ohms

b) energy decipated =   560J

Explanation:

V = I . R

R = V / I

R `= 70 / 20

R `= 3.5 ohms

2)energy decipated = 1/2ij²

energy decipated = 1/2 x 2.8 x (20)²

energy decipated =   560J

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A rod of mass M = 2.95 kg and length L can rotate about a hinge at its left end and is initially at rest. A putty ball of mass m
madam [21]

Answer:

Explanation:

angular momentum of the putty about the point of rotation

= mvR   where m is mass , v is velocity of the putty and R is perpendicular distance between line of velocity and point of rotation .

= .045 x 4.23 x 2/3 x .95 cos46

= .0837 units

moment of inertia of rod = ml² / 3 , m is mass of rod and l is length

= 2.95 x .95² / 3

I₁ = .8874 units

moment of inertia of rod + putty

I₁ + mr²

m is mass of putty and r is distance where it sticks

I₂  = .8874 + .045 x (2 x .95 / 3)²

I₂ = .905

Applying conservation of angular momentum

angular momentum of putty = final angular momentum of rod+ putty

.0837 = .905 ω

ω is final angular velocity of rod + putty

ω = .092 rad /s .

4 0
2 years ago
What is the average momentum of a 70-kg runner who covers 400 m in 50 s?
kykrilka [37]

Answer:

560 kg m/s

Explanation:

First of all, we have to find the velocity of the runner, which is given by  the ratio between the distance covered (400 m) and the time taken (50 s):

v=\frac{d}{t}=\frac{400 m}{50 s}=8 m/s

And now we can calculate the average momentum of the runner, which is equal to the product between the mass of the runner (70 kg) and its velocity, that we have previously calculated:

p=mv=(70 kg)(8 m/s)=560 kg m/s

8 0
2 years ago
What factors affect the ability of a substance to transfer thermal energy to heat or be heated by it's surroundings?
xeze [42]

The prime factors that affect the ability of substances to transfer the thermal energy to heat are the temperature difference between the two objects, area of cross-section, time, and distance travelled by the thermal energy.

<u>Explanation: </u>

The process of heat conduction takes place through contact between two or more objects. But this conduction depends on multiple factors that are responsible for thermal conduction. They are-

  • Temperature Difference(\Delta T) - The two objects must have a temperature difference else there will be no thermal conduction between them. The more the difference in their temperatures, the more thermal energy flows from one object to the other.
  • Area of Cross-section (A) - Larger areas of contact provide as better medium of thermal conduction.
  • Time (t) - The more time we give for the thermal conduction, the more energy is transmitted from one system to the other.
  • Distance Travelled (l) - The longer the distance, lesser the conduction. Means, the distance should be minimized in order to achieve the optimum thermal conduction between two objects.

Consider metal pot and its handle, it is being boiled for 15 m. The molecules present near the source of heat, showing fast vibration and bounce off. It actually indicates the heats of substance. That’s why, handle remains hot as heat conduction takes place.  It can be estimated by,

                                       Q=\frac{k A \Delta T t}{l}

k - Thermal conductivity of the material, measured in J/s.m.^{\circ} \mathrm{C}

4 0
2 years ago
a motorist traveling at 18m/s approaches traffic lights when he is 30 m from the stop line they turn red it takes 0.7 s before h
Gelneren [198K]

Answer:

35.2m

Explanation:

S= V^2 - U^2 ÷ 2A

S= (0) - (18) ÷ 2(4.6)

S= 324 ÷ 92

S= 35.2m

7 0
2 years ago
It takes 146./kjmol to break an oxygen-oxygen single bond. calculate the maximum wavelength of light for which an oxygen-oxygen
erastova [34]
To answer this question, we will use the following rule:
E = hc / lambda where:
E is the energy = 146 kJ/mol = 146000 J/mol
h is Planck's constant = 6.62*10^-34 kg m^2 / sec
c is the speed of light = 3*10^8 m/sec
lambda is the wavelength that we need to calculate 

Substitute with the given values in the above equation to get lambda as follows:
146000 = (6.62 * 10^-34 * 3 * 10^8) / lambda
lambda = 1.36*10^-30 meters
8 0
2 years ago
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