Defensive strategies focus on ways to score points against the opposing team.

Which of the following elements do living things have that volcanic rocks don’t have? A) Oxygen B) Silicon C) Magnesium D) Carbo

Mrrafil [7]

Either A or D. If I were answering I'd go with my git answer and say A

5 0

4 years ago

A transformer supplies 60 watts of power to a device that is rated at 20 volts. The primary coil is connected to a 120-volt ac s

Nataly [62]

Answer:

I = 0.5 A

Explanation:

Given: P=60 Watts, Voltage supply V = 120 Volts (for primary coil)

Solution:

we have P = V I

⇒ I = P /V = 60 Watts / 120 Volts

I = 0.5 A

4 0

3 years ago

An automobile travels on a straight road for 42 km at 45 km/h. it then continues in the same direction for another 42 km at 90 k

Nina [5.8K]

Answer:

a) The average velocity is v = (60 km/h ; 0)

b) The average speed is 60 km/h

Explanation:

The velocity is a vector that has a magnitude and direction. The average speed is the distance traveled over time without taking into account the direction of the motion.

a)The average velocity is calculated as the displacement over time:

v = Δx/Δt

where

v = velocity

Δx = final position - initial position = traveled distance relative to the center of the reference system.

Δt = final time - initial time (initial time is usually = 0)

We know that the displacement is 84 km but we do not know the time. It can be calculated from the two parts of the trip.

In part 1:

v = 45 km/h = 42 km / t

t = 0.93 h

In part 2:

v = 90 km/h = 42 km / t

t = 42 km / 90 km/h

t = 0.47 h

The time of travel is 0.47 h + 0.93 h = 1.4 h

The average velocity will be:

v = 84 km / 1.4 h = 60 km/h

Expressed as a vector in a 2-dimension plane:

v = (60 km/h; 0)

b) The average speed is calculated as the distance traveled over time. Note that in this case, the distance is equal to the displacement since the direction of the motion is always in one direction. But if the direction of the second part of the trip would have been the opposite to the direction of the first part, the displacement would have been 0 (final position - initial position = 0, because final position = initial position), then, the average velocity would have been 0. In change, the average speed would have been the distance traveled (84 km, 42 km in one direction and 42 km in the other) over time.

Then:

average speed = 84 km / 1.4 h = 60 km/h

c) see attached figure.

5 0

3 years ago

A stunt driver wants to make his car jump over 8 cars parked side by side below a horizontal ramp.

Genrish500 [490]

<u>Answer:</u>

a) Minimum speed must he drive off the horizontal ramp = 39.78 m/s

b) Minimum speed must he drive off the horizontal ramp with 7° above the horizontal = 23.93 m/s

<u>Explanation:</u>

a) The height of ramp = 1.5 meter

Horizontal distance he must clear = 22 meter

The car is having horizontal motion and vertical motion. In case of vertical motion the acceleration on the car is acceleration due to gravity.

We have equation of motion, $s= ut+\frac{1}{2} at^2$ , s is the displacement, u is the initial velocity, a is the acceleration and t is the time.

In case of vertical motion initial velocity = 0 m/s, acceleration = 9.8 $m/s^2$ , we need to calculate time when displacement = 1.5 meter.

$1.5=0*t+\frac{1}{2} *9.8*t^2\\ \\ t = 0.553 seconds$

So the car has to cover a distance of 22 meter in 2.119 seconds.

So minimum speed required = 22/0.553 = 39.78 m/s

Minimum speed must he drive off the horizontal ramp = 39.78 m/s

b) When the take of angle is 7⁰ the vertical speed of car is not zero = V sin 7 = 0.122 V

So the in case of vertical motion we have initial velocity = 0.122 V, S = -1.5 meter( below ramp), acceleration = -9.8 $m/s^2$

Substituting

$-1.5=0.122V*t-\frac{1}{2} *9.8*t^2\\ \\ 4.9t^2-0.122Vt-1.5=0$

In case of horizontal motion

Horizontal speed of car = V cos 7 = 0.993V

So it has to travel 22 meter in t seconds

0.993Vt = 22, Vt = 22.155 m

Substituting in the equation $4.9t^2-0.122Vt-1.5=0$

We will get $4.9t^2-0.122*22.155-1.5=0\\ \\ t = 0.926 seconds$

Speed required = 22.155/0.926 = 23.93 m/s

Minimum speed must he drive off the horizontal ramp with 7° above the horizontal = 23.93 m/s

7 0

3 years ago

Waste from nuclear power plants must be disposed of in radioactively shielded storage containers. Please select the best answer

Andreas93 [3]

Answer:

True

Explanation:

When a nuclear power plants ends its operating life, it is necessary to dispose correctly all the radioactive material left from the operations of the power plant.

In fact, apart from the fuel rods (which contain the uranium that is the fuel of the nuclear reactions), other materials of the core (such as the vessel) becomes radioactive due to the prolonged exposure to the products of nuclear reactions in the core.

As a result, all these materials remain radioactive for very long time (hundreds or thousands of years). It is therefore important to dispose them correctly, in proper sealed containers which are able to shield the radiation emitted by these radioactive element (alpha, beta and gamma radiation).

Therefore, "waste from nuclear power plants must be disposed of in radioactively shielded storage containers" is a correct statement.

7 0

3 years ago

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