In winter why do water tanks start freezing from surface and not from bottom

Two cars are traveling along perpendicular roads, car A at 40 mi/hr, car B at 60 mi/hr. At noon, when car A reaches the intersec

Serggg [28]

Answer:

$\frac{dD}{dt} = -4 miles/hour$

negative sign indicates that the distance is decreasing with time

Explanation:

Let at any time t after noon that is 12 p.m.

distance traveled by car A = 40t

distance traveled by car B = 90-60t

then distance between the two cars at time t

$D^2= (40t)^2+(90-60t)^2$ ............1

also, at time 1 p.m.

distance $D^2= (40\times1)^2+(90-60\times1)^2$

D=50 Km

differentiating equation 1 w.r.t. t we get

$2D\frac{dD}{dt}= 2\times40t\times40+2(90-60t)(-60)$

put t= 1 and D= 50 we get

$2\times50\frac{dD}{dt}= 3200\times1-3600\times1$

$\frac{dD}{dt} = -4 miles/hour$

3 0

3 years ago

To have a change in acceleration there has to be a change in velocity.

tresset_1 [31]

Answer: Compared to displacement and velocity, acceleration is like the angry, fire-breathing dragon of motion variables. It can be violent; some people are scared of it; and if it's big, it forces you to take notice. That feeling you get when you're sitting in a plane during take-off, or slamming on the brakes in a car, or turning a corner at a high speed in a go kart are all situations where you are accelerating.

7 0

3 years ago

Read 2 more answers

What charge does an atom have when electrons are lost from the atom?

maw [93]

Negative charge (it has more protons than electrons)

6 0

3 years ago

A water wave travels across a 42-meter wide pond in 7.0 seconds. The speed of the wave is _____. 292 m/s 49 m/s 6.0 m/s 0.17 m/s

tekilochka [14]

   Speed = (distance covered) / (time to cover the distance).

The speed of anything that covers 42 meters in 7 seconds is

   (42 meters) / (7.0 seconds)

   = (42 / 7.0) (meters/second)

   =   6.0 m/s .

7 0

3 years ago

Read 2 more answers

Pedro e Maria saíram para passear de carro. Eles partiram de São Paulo às 10 h em direção à Braúna, localizada a 500 km da capit

Salsk061 [2.6K]

Answer:

This can be translated to:

"P edro and Maria went for a drive. They left São Paulo at 10 am towards Braúna, located 500 km from the capital. As the journey was long, they made two 15-minute stops for gas and also spent 45 minutes for lunch. When arriving at the final destination, Maria looked at the clock and saw that it was 6 pm. What is the average speed of the trip?"

Ok, the first thing we know is, that for the average speed we can write:

Speed = Distance/time.

First, we know that Distance = 500km.

And for the time we have two possiblities:

The total average speed will decrease because they were stopped a total of:

15min + 15min + 45min = 75min = 1.25 hours

Then if the travel starts at 10am, and ends at 6 pm, the total time that has passed is:

6pm = 18hs

6pm - 10am = 18 - 10 = 8hs

Then the average speed will be:

Speed = 500km/8h = 62.5 km/h.

Now, if we considerate the average speed only when they are moving, the total time that they are moving is:

Total time in travel - time that they where stopped

8h - 1.25h = 6.75h

Then the average speed would be:

Speed = 500km/6.75h = 74.1 km/h

4 0

3 years ago