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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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5. An undisturbed soil sample has a wet density of 2.5 Mg/m3 when the water content is 25%. The specific gravity of the soil par

Dima020 [189]

Answer:

The submerged effective density is 86.93 kN/m³ or 8.693 Mg/m³

Explanation:

Given;

wet density of soil sample = 2.5 Mg/m³ = 25 kN/m³

Specific gravity of solid particle = 2.7

The dry unit weight of soil;

$\gamma _d = \frac{\gamma _t}{1 +w} = \frac{25}{1+0.25} = 20 \ kN/m^3$

for undisturbed state, the volume of the soil is;

$V_s =\frac{\gamma _d}{G_s \gamma _w} = \frac{20}{2.7*9.81} = 0.76 \ m^3\\\\Void \ volume, V_v = 1-0.76 = 0.24 \ m^3$

$Void \ ratio, \ e = \frac{0.24}{0.76} = 0.32$

Submerged effective density is given as;

$\rho _b = \frac{\rho_w(\gamma_s -1)}{1+e}$

density of water (ρw) = 2.7 x 25 kN/m³ = 67.5 kN/m³, substitute this in the above equation;

$\rho _b = \frac{\rho_w(\gamma_s -1)}{1+e} = \frac{67.5(2.7 -1)}{1+0.32} = 86.93 \ kN/m^3$

Therefore, the submerged effective density is 86.93 kN/m³ or 8.693 Mg/m³

5 0

3 years ago

An unwary football player collides with a padded goalpost while running at a velocity of 9.50 m/s and comes to a full stop after

Amanda [17]

Answer:

(a) The collision lasts for 0.053 s.

(b) The deceleration is 180.5 m/s².

Explanation:

Given:

Initial velocity of the player (u) = 9.50 m/s

Final velocity of the player (v) = 0 m/s (Comes to a stop)

Displacement of the player (S) = 0.250 m

We know that, using equation of motion relating displacement (S), acceleration (a), initial velocity (u) and final velocity (v), we have:

$v^2=u^2+2aS$

Expressing in terms of 'a', we get:

$a=\frac{v^2-u^2}{2S}$

Plug in the given values and solve for 'a'. This gives,

$a=\frac{0-9.50^2}{2\times 0.250}\\\\a=\frac{-90.25}{0.5}=-180.5\ m/s^2$

Therefore, the acceleration of the player is -180.5 m/s². So, the deceleration is 180.5 m/s².

Now, using the first equation of motion, we have:

$v=u+at\\\\t=\frac{v-u}{a}$

Plug in the given values and solve for 't'. This gives,

$t=\frac{0-9.5}{-180.5}\\\\t=0.053\ s$

Therefore, the the collision will last for 0.053 s.

(a) The collision lasts for 0.053 s.

(b) The deceleration is 180.5 m/s².

8 0

3 years ago

Colonel John P. Stapp, USAF, participated in studying whether a jet pilot could survive emergency ejection. On March 19, 1954, h

PolarNik [594]

Answer:

(a) a = - 201.8 m/s²

(b) s = 197.77 m

Explanation:

(a)

The acceleration can be found by using 1st equation of motion:

Vf = Vi + at

a = (Vf - Vi)/t

where,

a = acceleration = ?

Vf = Final Velocity = 0 m/s (Since it is finally brought to rest)

Vi = Initial Velocity = (632 mi/h)(1609.34 m/ 1 mi)(1 h/ 3600 s) = 282.53 m/s

t = time = 1.4 s

Therefore,

a = (0 m/s - 282.53 m/s)/1.4 s

a = - 201.8 m/s²

(b)

For the distance traveled, we can use 2nd equation of motion:

s = Vi t + (0.5)at²

where,

s = distance traveled = ?

Therefore,

s = (282.53 m/s)(1.4 s) + (0.5)(- 201.8 m/s²)(1.4 s)²

s = 395.54 m - 197.77 m

s = 197.77 m

6 0

3 years ago

Read through the and calculate the predicted change in kinetic energy of the oblect compared to 50 kg ball traveling at 10 m/s .

Sliva [168]

Answer:

A 50 kg ball traveling at 20 m/s would have 4 times more kinetic energy.

A 50 kg ball traveling at 5 m/s would have 4 times less kinetic energy.

A 50 kg person falling at 10 m/s would have the same kinetic energy.

Explanation:

hope this helps:)

5 0

3 years ago

Why do you think it is a driving force of weather around the world?

Finger [1]

Answer:

The sun.

Explanation:

The sun provides energy for living organisms, and it drives our planet’s weather and climate patterns.

Remember, Earth is spherical and the energy from the sun does not reach all areas with equal intensity. Areas exposed to the sun are directly on the sun’s rays (i.e. those nearest to the equator) and hence, receive greater solar input. In contrast, those in higher latitudes receive sunlight that is spread over a larger area and that has taken a longer path through the atmosphere. As a result, these higher latitudes receive less solar energy.

Also, ocean circulation and precipitation are all factors of weather

4 0

3 years ago