What are some charactersitics of pressure waves

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

A 77.0−kg short-track ice skater is racing at a speed of 12.6 m/s when he falls down and slides across the ice into a padded wal

sukhopar [10]

Answer:

-6112.26 J

Explanation:

The initial kinetic energy, $KE_i$ is given by

$KE_i=0.5mv_1^{2$ } where m is the mass of a body and $v_i$ is the initial velocity

The final kinetic energy, $KE_f$ is given by

$KE_f=0.5mv_f^{2}$ where $v_f$ is the final velocity

Change in kinetic energy, $\triangle KE$ is given by

$\triangle KE=KE_f-KE_i=0.5mv_f^{2}-0.5mv_1^{2}=0.5m(v_f^{2}-v_i^{2})$

Since the skater finally comes to rest, the final velocity is zero. Substituting 0 for $v_f$ and 12.6 m/s for $v_i$ and 77 Kg for m we obtain

$\triangle KE=0.5*77*0^{2}-0.5*77*(0^{2}-12.6^{2})=-6112.26 J$

From work energy theorem, work done by a force is equal to the change in kinetic energy hence for this case work done equals <u>-6112.26 J</u>

3 0

2 years ago

Anyone know what the answer is?..

Licemer1 [7]

Answer:

sometimes harmful and sometimes beneficial

8 0

3 years ago

Your father bought you a pair of shoes. When you wore the shoes you realized there was a problem. The shoes were too long. Why m

Elenna [48]

Answer: This problem may arise when your father never bought a shoe before. A male is bad at buying accesories and guessing the size, so the mother should have bought a pair of shoes. Or it can also be that your father has a short term memory or that he never knew the size of your feets. The feet might also have irregular growth for which it grows more than the normal size but such cases are rare to be seen.

You can prevent this by going with your father and selecting the shoe of your size. Or you can simply send your mother to buy it for you instead. Or another perfect choice could be is that you just dont ever send your father to buy anything for you or just never buy a pair of shoes. Wear the shoes that you always did or buy it yourself since your the one who is supposed to know the size of your feets. Another possible solution could be that you can make use of the money by gifitng them to someone close to you.

5 0

2 years ago

a pool ball leaves a 0.60 meter high table with an initial high table with an initial horizontal velocity of 2.4m/s. predict the

timurjin [86]

Ball leaves the table of height 0.60 m

Initial speed of the ball is in horizontal direction which is 2.4 m/s

Now here we can say that time taken by the ball to hit the ground will be given by kinematics equation in vertical direction

$\Delta y = v_y*t + \frac{1}{2}at^2$