PHYSICS HIGH SCHOOL

A motorist is driving at 20m/s when she sees that a traffic light 200m ahead has just turned red. She knows that this light stays red for 15s, and she wants to reach the light just as it turns green again. It takes her 1.0s to step on the brakes and begin slowing. What is her speed as she reaches the light at the instant it turns green?

Answers

Answer 1

Answer:

8.57 m/s

Explanation:

let's list out available parameters:

Initial velocity, u = 20 m/s

Time = 15 - 1 = 14 s

Distance, s = 200 m

Final velocity = ?

We are assuming a uniformly accelerated motion.

Using one of the equations of motion $s = \left((u+v)/(2)\right)t$

$v = (2s)/(t)-u$

$v=(2*200)/(14)-20$

$v=28.6 - 20$

$v=8.6$ m/s

Answer 2

Answer:

Final answer:

To stop just as the light turns green, the motorist needs to decelerate in a controlled manner. The effective time to cover the distance after seeing the red light is 14 seconds, disregarding the 1 second it takes to react and press the brakes. Therefore, as she reaches the traffic signal when it turns green, her speed is 0 m/s.

Explanation:

This situation can be approached using the concept of kinematics in Physics. To solve it, we need to consider total time and total distance traveled. The motorist is driving towards the traffic light, which is 200m away, and the light stays green for 15 seconds. However, since it takes her 1 second to step on the brakes, effectively, she has 14 seconds to travel to the light.

Since she starts braking the car, she begins to decelerate. While decelerating, time is the only determinant of the distance covered, not the speed. As she reaches the light, the speed would be zero regardless of the initial speed or distance if the deceleration is constant. So, when the light turns green, her speed will be 0 m/s.

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Consider a mixture of air and gasoline vapor in a cylinder with a piston. The original volume is 40. cm3. If the combustion of this mixture releases 950. J of energy, to what volume will the gases expand against a constant pressure of 650. torr if all the energy of combustion is converted into work to push back the piston

Answers

The given system is a constant pressure systemwhere the work done is the product of the pressure and the volume change.

The volume to which the gas expands to is approximately 11 liters

Reasons:

Given parameters;

The original volume, V₁ = 40 cm³

The energy released, E = 950 J

Constant pressure applied, P = 650 torr.

Condition: All energy is converted to work to push back the piston

Required:

The volume to which the gas will expand

Solution;

The work done, W = Energy releases, E = 950 J

Work done at constant pressure, W = P·(V₂ - V₁)

Where;

V₂ - The volume to which the gas will expand

Converting the volume to from cm³ to m³ gives;

V₁ = 40 cm³ = 0.00004 m³

Converting the pressure given in torr to Pascals gives;

650 torr. = 86659.54 Pa.

Therefore, we get;

950 J = 86659.54 Pa. × (V₂ - 0.00004 m³)

$V_2 = (950 \, J)/(86659.54 \, Pa) + 0.00004 \, m^3 = (2888)/(263445) \ m^3 + 0.00004 \, m^3 = (2683)/(243855) \, m^3$

Converting to liters gives;

$V_2 =(2683)/(243855) \, m^3 * (1,000 \, l )/(m^3) \approx 11.00244\, l \approx 11 \, l$

The volume to which the gas expands, V₂ ≈ 11 liters.

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Answer:

The volume needed to expand the gas is = 11 Lit = 11000 $cm^(3)$

Explanation:

Given :

Initial volume $V_(1) = 40 cm^(3) = 0.04$ Lit.

Energy $W = 950$ J = 9.38 Lit × atm. ⇒ ( 1 Lit×atm. = 101.325 J )

Pressure $P =$ 650 torr = 0.855 atm. ⇒ ( 1 torr = 0.00132 atm )

In this example we have to be aware of unit conversion system.

From the laws of thermodynamics,

$W = P \Delta V$

Here in this example, all the energy of combustion is converted into work to push back the piston

$W = P (V_(2) - V_(1) )$

$V_(2) - 0.04 = 10.96$

$V_(2) = 11$ Lit = $11000 cm^(3)$

The highest point of a wave is called thea. height.
b. trough.
c. crest.
d. wavelength

Answers

The highest point of a wave is called the "crest." A wave is a disturbance that travels through a medium or space, transferring energy without transporting matter. Therefore, the correct answer is option c.

As a wave propagates, it undergoes cycles of oscillation with alternating high and low points. The highest point of a wave, where the displacement or amplitude is at its maximum, is referred to as the "crest." On the other hand, the term "trough" refers to the lowest point of a wave, where the displacement or amplitude is at its minimum in the negative direction. The trough is the opposite of the crest, representing the bottommost part of a wave.

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the answer is c , crest

When two objects collide, they experience the exact same amount of force in opposite directions.O True
O False

Answers

Answer:

True

Explanation:

In a collision between two objects, both objects experience forces that are equal in magnitude and opposite in direction. Such forces often cause one object to speed up (gain momentum) and the other object to slow down (lose momentum).

true because they experience the force from the other object, and the other experiences its force.

One major cause of floods isA. rapid spring snowmelt.
B. light rain over a large area.
C. a decrease in stream discharge.
D. increased capacity of stream channels.

Answers

The correct answer is A. rapid spring snowmelt. When the spring times come, sometimes there's a lot of warmth that suddenly comes, especially nowadays when there's things such as global warming. So the snow melts and large amounts of water can flood the fields that are often found at the foot of a mountain or similar things.

The answer to this question is A. Rapid Spring Snowmelt. You can find the answer in Pearson Earth Science Part 1 Textbook. "A heavy downpour or rapid snowmelt can flood canyons with a mixture of soil, rock, and water."

Hope this helps. Have a great day!

36 The height of a 30-story building is approximately(1) 10^0 m (3) 10^2 m
(2) 10^1 m (4) 10^3 m

Answers

An approximation used to measure building height is 10 feet per building level.

Converting from feet to meters using the equation:
1 ft = 0.3048m
10 ft = 3.048m

Multiplying that by 30 storeys, we get:
3 x 3.048m = 91.44m, which is near the answer of (3) 10^2 m or 100m.

Height of cannon 5 m, initial speed of projectile 15m/s, angle of launch 0 degrees. What is the range and time in the air? Please show work!

Answers

Answer:

The range is 15.15 m and the time in the air is 1.01 s

Explanation:

Horizontal Motion

When an object is thrown horizontally (with angle 0°) with a speed v from a height h, it follows a curved path ruled exclusively by gravity until it eventually hits the ground.

The range or maximum horizontal distance traveled by the object can be calculated as follows:

$\displaystyle d=v\cdot\sqrt{\frac {2h}{g}}$