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3 years ago

Help me please :(((((((

Physics

2 answers:

Dimas [21]3 years ago

5 0

Answer: A.

Explanation: Roughly 180 - 200 million years ago, just before the first dinosaurs evolved. Mammals themselves evolved from a group or reptiles which exhibited mammal-like traits. One of them was specialized teeth. Reptiles tend to have teeth all the same shape. The mammal-like reptiles evolved tiny teeth in front of the jaw and two pairs of over sized fangs along the the sides. Like modern mammals, the head was large in proportion to the rest of the body. The jaws were also evolving another mammal trait, the ability to move sideways. Despite the lack of specialized teeth, acute hearing and the ability to chew, the dinosaurs evolved an adaptation which made them far more successful than mammals--modified leg bones. These limbs could be articulated directly under their bodies. This enabled the legs to support more weight, since the limbs were now under the body instead of at the sides. Then dinosaurs did something which secured their dominance for the next 120 million years - they began to stand on two legs. Although the back was still parallel to the ground, running on two legs greatly increased the dinosaur's speed. Mammals could simply not compete with swift, giant predators and were forced to remain small, and most became nocturnal to evade dinosaurs which were probably active during the day. Despite that they managed to survive which allowed the further evolution of mammals into us, humans.

sveta [45]3 years ago

5 0

In the Cenozoic period only mammals were alive. All dinosaurs had gone extinct leaving animals such as cave lions, woolly mammoths, and cave bears. Considering that Dinosaurs had gone extinct roughly 66 million years ago in the Cretaceous era and the Cenozoic era was 66 million years ago, the beginning of the Cenozoic era started with the extinction of dinosaurs.

Answer: D

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A parallel-plate capacitor with plates of area 540 cm2 is charged to a potential difference V and is then disconnected from the

notsponge [240]

Answer: 0.8 nC

Explanation: In order to explain this problem we have top use the expression for the capacitor of parallel plates, which is given by:

C=εo*A/d where A and d are the area and the separation of the plates.

Then we have

V=Q/C so ΔV= Q* Δd/(εo*A)

Q= 100* 0.054*8.85*10^-12/( 0.06)=0.8 nC

5 0

3 years ago

Chris shoots an arrow up into the air. The height of the arrow is given by the function h(t) = - 16t2 + 32t + 26 where t is the

seropon [69]

Answer:

The maximum height of the arrow is 42 (and the units given for the height)

Explanation:

Everything is easier if you make a graph, you can give values to t and replace that values in the function, for example:

When t=0

$h(0)=-16(0^{2})+32(0)+26$

h(0)=26

If you give some values to t you can see how the trajectory of the arrow is (please look the graphic below)

Now, to find the maximum you have to find the derivative of the function that describes the height of the arrow:

$h(t)=-16t^{2}+32t+26$

$h'(t)=-32t+32$

Then you have to take the derivative, and equals to zero to find t:

-32t+32=0

-32t=32

t=1

That is in the time of 1 second the arrow has its maximum height.

Now you have to replace this value in the original function, to find the height of the arrow:

$h(1)=-16(1^{2})+32(1)+26$

h(1)=-16+32+36

h(1)=42

4 0

3 years ago

The radar gun measures the frequency of the radar pulse echoing off your car. By what percentage is the measured frequency diffe

mel-nik [20]

Question: A. The state highway patrol radar guns use a frequency of 9.15 GHz. If you're approaching a speed trap driving 30.1 m/s, what frequency shift will your FuzzFoiler 2000 radar detector see?

B. The radar gun measures the frequency of the radar pulse echoing off your car. By what percentage is the measured frequency different from the original frequency? (Enter a positive number for a frequency increase, negative for a decrease. Just enter a number, without a percent sign.)?

Answer:

The frequency change percentage is 9.94%

Explanation:

The frequency shift can be calculated as follows.

$F= \frac{V+V_{0}}{V+V_{s}}$

= $9.05GHz\times\frac{343m/s+0}{343m/s+(-31.3m/s)}$

=9.95 GHz

So the frequency change seen by the detector is 9.95 - 9.05

% difference $= \frac{0.9}{9.05} \times100$

= 9.94%

3 0

2 years ago

Two stunt drivers drive directly toward each other. At time t=0 the two cars are a distance D apart, car 1 is at rest, and car 2

lesantik [10]

Answer: Hello there!

We know this:

The distance between the cars at t= 0 is D.

car 2 has an initial velocity of v0 and no acceleration.

car 1 has no initial velocity and a acceleration of ax that starts at t = 0

then we could obtain the acceleration of the car 1 by integrating the acceleration over the time; this is v(t) = ax*t where there is not a constant of integration because the car 1 has no initial velocity.

Because the cars are moving against each other, we want to se at what time t they meet, this is equivalent to see:

position of car 1 + position of car 2 = D

and in this way we could ignore constants of integration :D

for the position of each car we integrate again:

P1(t) = (1/2)ax*t^2 and P2(t) = v0t

v0t + (1/2)ax*t^2 = D

v0t + (1/2)ax*t^2 - D = 0

now we can solve it for t using the Bhaskara equation.

$t = \frac{-v0 +\sqrt{v0^{2} + 4*(1/2)ax*D } }{2(1/2)ax} =\frac{-v0 +\sqrt{v0^{2} + 2ax*D } }{ax}$

that we cant solve witout knowing the values for v0, D and ax. But you could replace them in that equation and obtain the time, where you must remember that you need to choose the positive solution (because this quadratic equation has two solutions).

Now we want to know the velocity of car 1 just before the impact, this can be calculated by valuating the time in the as the time that we just found in the velocity equation for the car 1, this is:

$v(\frac{-v0 +\sqrt{v0^{2} + 2ax*D } }{ax}) = ax*\frac{-v0 +\sqrt{v0^{2} + 2ax*D } }{ax} = {-v0 +\sqrt{v0^{2} + 2ax*D }$

where again, you need to replace the values of v0, D and ax.

7 0

3 years ago

What’s is the movement of one object around another

allsm [11]

Answer:

revolution

Explanation:

8 0

3 years ago