I. The substance in model A has the highest density.

A dockworker loading crates on a ship finds that a 21-kg crate, initially at rest on a horizontal surface, requires a 73-N horiz

Nataliya [291]

1) Static friction coefficient: 0.355

The crate is initially at rest. The crate remains at rest until the horizontal pushing force is less than the maximum static frictional force.

The maximum static frictional force is given by

$F_s = \mu_s mg$

where

$\mu_s$ is the static coefficient of friction

m = 21 kg is the mass of the crate

g = 9.8 m/s^2 is the acceleration due to gravity

The horizontal force required to set the crate in motion is 73 N: this means that this is the value of the maximum static frictional force. So we have

$F_s=73 N$

Using this information into the previous equation, we can find the coefficient of static friction:

$\mu_s = \frac{F}{mg}=\frac{73 N}{(21 kg)(9.8 m/s^2)}=0.355$

2) Kinetic friction coefficient: 0.267

Now the crate is in motion: this means that the kinetic friction is acting on the crate, and its magnitude is

$F_k = \mu_k mg$ (1)

where

$\mu_k$ is the coefficient of kinetic friction

There is a horizontal force of

F = 55 N

pushing the crate. Moreover, the speed of the crate is constant: this means that the acceleration is zero, a = 0.

So we can write Newton's second law as

$F-F_k = ma = 0$

And by substituting (1), we can find the value of the coefficient of kinetic friction:

$F-\mu_k mg = 0\\\mu_k = \frac{F}{mg}=\frac{55 N}{(21 kg)(9.8 m/s^2)}=0.267$

5 0

3 years ago

Which of the following statements about insulating materials is correct?a.Insulators can be used to increase the amount of curre

dimulka [17.4K]

Answer:

a.Insulators can be used to increase the amount of current that can flow through a resistor without increasing its temperature.

Explanation:

A conductor has low resistance, while an insulator has much higher resistance. Devices called resistors control amounts of resistance into an electrical circuits. Electric charges inside an insulator are bound to the individual atoms or molecules, not being able to move inside the material.

When you turn up the resistance, the electric current flowing through the circuit is reduced

Ohm's law:

V = I * R

R = V/I

An Ohmic conductor would have a linear relationship between the current and the voltage. With non-Ohmic conductors, the relationship is not linear. Most metals are good conductors example silver, copper etc.

6 0

3 years ago

If an object with a mass of 30 kg accelerates at a rate of 2 m/s^2, what is the

Zolol [24]

Hello, for this use the second law of Newton:

F = ma

We have the data:

F = ?

m = 30 kg

a = 2 m/s^2

Replacing:

F = 30 kg * 2 m/s^2

F = 60 N

Result:

The force is of 60 Newtons.

8 0

3 years ago

What would we see if we were able to travel within the multiverse?

rodikova [14]

To be honest you would be able to see anything you wanted to see.

6 0

3 years ago

A bird is flying directly toward a stationary bird-watcher and emits a frequency of 1490 Hz. The bird-watcher, however, hears a

Eva8 [605]

Answer:

The speed of the bird is 1.00% of the speed of sound.

Explanation:

The speed of the bird can be found by using the Doppler equation:

$f = f_{0}(\frac{v - v_{r}}{v - v_{s}})$

Where:

v: is the speed of sound = 343 m/s

f₀: is the frequency emitted = 1490 Hz

f: is the frequency observed = 1505 Hz

$v_{r}$ : is the speed of the receiver = 0 (it is stationary)

$v_{s}$ : is the speed of the source =?

The minus sign of $v_{s}$ is because the source is moving towards the receiver.

By solving the above equation for $v_{s}$ we have:

$v_{s} = v - \frac{f_{0}*v}{f} = 343 - \frac{1490*343}{1505} = 3.42 m/s$

The above speed in terms of the speed of sound is:

$\% v_{s} = \frac{3.42}{343}\times 100 = 1.00 \%$

Therefore, the speed of the bird is 1.00% of the speed of sound.

I hope it helps you!

8 0

3 years ago