Are small molecular units joined together in large molecules

Question 27 a motorboat takes 3 hours to travel 144km going upstream. the return trip takes 2 hours going downstream. what is th

Vedmedyk [2.9K]

In this item, we let x be the rate of the boat in still water and y be the rate of the current.

Upstream. When the boat is going upstream, the speed in still water is deducted by the speed of the current because the boat goes against the water. The distance covered is calculated by multiplying the number of hours and the speed.
(x - y)(3) = 144

Downstream. The speed of the boat going downstream is equal to x + y because the boat goes with the current.
(x + y)(2) = 144

The system of linear equations we can use to solve for x is,
3x - 3y = 144
2x + 2y = 144

We use either elimination or substitution.

We solve for the y of the first equation in terms of x,
y = -(144 - 3x)/3

Substitute this to the second equation,
2x + 2(-1)(144 - 3x)/3 = 144
The value of x from the equation is 60

<em>ANSWER: 60 km/h</em>

5 0

3 years ago

An electric iron is connected to the mains power supply of 220 V. When the electric iron is

Ilya [14]

Answer:

Given: V = 220V, Pmin = 360W, Pmax = 840W

For minimum heating case:

We know that

Pmin = VI

360 = 220 X I

I = 1.63 amp

R = V/I

R = 220/1.63

R = 134.96ohms

For maximum heating case:

We know that

Pmax = VI

840 = 220 X I

I = 3.81 amp

R = V/I

R = 220/3.81

R = 57.74 ohms

7 0

2 years ago

What is the speed of a commercial jet which travels form New York to Los Angeles (4800) in 6 hours

Colt1911 [192]

Answer:

$Speed = 800km}/hr$

Explanation:

Given

$Distance = 4800km$

$Time = 6hr$

Required

Determine the speed of the jet

The speed is calculated as:

$Speed = \frac{Distance}{Time}$

Substitute 4800 km for Distance and 6hr for Time

$Speed = \frac{4800km}{6hr}$

$Speed = 800km}/hr$

<em>Hence, the speed of the commercial jet is 800km/hr</em>

8 0

2 years ago

A 10-cm-long wire is pulled along a u-shaped conducting rail in a perpendicular magnetic field. the total resistance of the wire

Debora [2.8K]

In the above case we can say that power given by external agent to pull the rod must be equal to the power dissipated in the form of heat due to magnetic induction.

Part a)

when we pull the rod with constant speed then power required will be product of force and velocity

here we will have

$P = F.v$

P = 4 W

v = 4 m/s

now we will have

$4 = F*4$

$F = 1N$

So external force required will be 1 N

PART B)

now in order to find magnetic field strength we can say

$P = \frac{v^2B^2L^2}{R}$

here we know that induced EMF in the wire is E = vBL

so power due to induced magnetic field is given by

$P = \frac{E^2}{R}$

$4 = \frac{4^2*B^2*0.10^2}{0.20}$

by solving above equation we will have

$B = 2.24 T$

5 0

3 years ago

A rifle that shoots bullets at 477 m/s is to be aimed at a target 45.5 m away. If the center of the target is level with the rif

Free_Kalibri [48]

Answer:

The rifle barrel must be pointed at a height of 4.45cm above the target so that the bullet hits dead center.

Explanation:

First, we need to sketch the situation so we can have a better idea of what the problem looks like (Refer to uploaded picture).

So as you may see in the drawing, when pointing the rifle to the target, we can see it as a triangle, but in reality, the bullet will have a parabolic trajectory. Both points of view will help us determine what the height must be. In order to find it, we need to first determine at what angle the bullet should be shot. In order to do so we can use the range formula, which looks like this:

$R=\frac{v^{2}sin(2\theta)}{g}$

Where R is the range of the bullet (this is how far it goes before it has the

same height it was shot from), v is the original speed of the bullet, θ is the angle at which the bullet is shot and g is the acceleration of gravity.

We can solve this equation for theta, so we get:

$gR=v^{2}sin(2\theta)$