Here’s the formula for an exponential RC discharge.

(If you were not a Brainly robot, you would have seen this formula before,
in any class that would assign you this problem to solve.)

Charge = (initial charge) · e ^ -(time / RC) .

In this situation:

0.1  =  (1) · e ^ -(.0025 / 2.8R x 10⁻⁶)

Ln of each side:            ln(0.1) = -.0025 / 2.8R x 10⁻⁶

Multiply each side
by R                            R · ln(0.1)  =  -.0025 / 2.8 x 10⁻⁶

Divide each side
by  ln(0.1) = -2.303:      R  =  0.0025 / (2.303 · 2.8 x 10⁻⁶)

I get     387.8 Ω

## Related Questions

Posted in Physics

What is the force between two charged objects

It’s called the ‘Electrostatic Force’.

It’s proportional to the product of their charges, and
inversely proportional to the square of the distance
between them.

It pulls them together if their charges are opposite.
It pushes them apart if they have the same charge.

Posted in Physics

A 60-W light bulb radiates electromagnetic waves uniformly in all directions. At a distance of 1.0 m from the bulb, the light intensity is I0, the average energy density of the waves is u0, and the rms electric and magnetic field values are E0 and B0, respectively. 1. At 2.0 m from the bulb, what is the light intensity? 2. At 2.0 m from the bulb, what is the rms magnetic field value? 3. At 2.0 m from the bulb, what is the average energy density of the waves?

1. If we increase the distance to twice it’s original value, the light intensity is reduced by one-fourth, the light intensity would be:
I0/4

2. rms magnetic field is inversely proportional to distance, so the new rms magnetic field would be:
B0/2

3. average energy density is inversely proportional to the square of the distance, so the new average energy density is:
E0/4

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Posted in Physics

At t = 0, one toy car is set rolling on a straight track with initial position 13.5 cm, initial velocity -4.2 cm/s, and constant acceleration 2.60 cm/s2. At the same moment, another toy car is set rolling on an adjacent track with initial position 8.5 cm, initial velocity 5.20 cm/s, and constant zero acceleration. (a) At what time, if any, do the two cars have equal speeds? (b) What are their speeds at that time? (c) At what time(s), if any, do the cars pass each other? …?

(a) We must first look at the formulas of the velocities of each toy car. v1 =
-4.2 + 2.60t. v2 = 5.20. When the two cars have equal speed, then
v1 = v2
-4.2 + 2.60t = 5.20
2.60t = 9.40
t = 3.62 s

(b) Their speed would then be 5.20 m/s. The toy car does not change speed since it doest not have any acceleration.
(c) The two cars will pass each other when their positions are equal.
x1 = 13.5 – 4.2t + 0.5*2.60t^2
x2 = 8.5 + 5.20t
x1 = x2
13.5 – 4.2t + 1.30t^2 = 8.5 + 5.20t
1.30t^2 – 9.40t + 5.0 = 0
t = 6.65s or t = 0.58 s

——————–

I hope my answer has come to your help. Thank you for posting your question here in Brainly. We hope to answer more of your questions and inquiries soon. Have a nice day ahead!

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Posted in Physics

“A copper wire loop is constructed so that its radius, r, can change. It is held near a solenoid that has a constant current through it. a. Suppose that the radius of the loop were increasing. Use Lenz’ law to explain why there would be an induced current through the wire. Indicate the direction of that current. b. Check your answer regarding the direction of the induced current by considering the magnetic force that is exerted on the charge in the wire of the loop. ” “A copper wire loop is constructed so that its radius, r, can change. It is held near a solenoid that has a constant current through it. a. Suppose that the radius of the loop were increasing. Use Lenz’ law to explain why there would be an induced current through the wire. Indicate the direction of that current. b. Check your answer regarding the direction of the induced current by considering the magnetic force that is exerted on the charge in the wire of the loop. “

a. There is a constant magnetic Feld, which means B is constant, so we can rewrite the change in fux as above.Because ΔA is positive, there will be a negative emf in the loop, corresponding to an induced magnetic momentpointing to the left on the page. The current in the loop will be into the page at the top and out of the page atthe bottom

V=-Δφ/ Δt = -B·ΔA/ Δt

b. As the loop’s radius is increasing, we can think about individual electrons in the wire loop as moving radiallyoutward. We’ll consider one in the top of the loop (which is moving up the page). Using the Lorentz ²orce Law

F=q(~v⇥~B)=qvB(ˆy⇥ˆx)=-qvBˆ

Constant forces pointing into the center of the loop will result in circular orbits (around the wire). Because theforce is pointing into the center of the loop, we know we have positive current at that point (into the page).

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Posted in Physics

A car with a mass of 1,324 kilograms, traveling at a speed of 20 meters/second, crashes into a wall and stops. What is the kinetic energy after this perfectly inelastic collision? A. 0.0 joules B. 3.2 × 103 joules C. 1.0 × 104 joules D. 1.3 × 104 joules …?

A. 0.0 joules

Explanation:

We can calculate the initial kinetic energy of the car, which is given by:

where m is the mass of the car and v its initial speed. After the collision, the car stops, so its final speed is zero. Therefore, the new kinetic energy of the car will be

This type of collision is called ‘perfectly inelastic collision’, and it occurs when there is the maximum loss of kinetic energy, as in this case. Therefore, the correct answer is

A. 0.0 joules

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