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aivan3 [116]
3 years ago
6

A car is driving at 85 km/h and the driver spots a stop sign ahead. What coefficient of friction is needed to stop the car at th

e stop sign if the stop sign is 900m away?
Physics
1 answer:
almond37 [142]3 years ago
5 0

Answer:

μ = 0.0315

Explanation:

Since the car moves on a horizontal surface, if we sum forces equal to zero on the Y-axis, we can determine the value of the normal force exerted by the ground on the vehicle. This force is equal to the weight of the cart (product of its mass by gravity)

N = m*g (1)

The friction force is equal to the product of the normal force by the coefficient of friction.

F = μ*N (2)

This way replacing 1 in 2, we have:

F = μ*m*g (2)

Using the theorem of work and energy, which tells us that the sum of the potential and kinetic energies and the work done on a body is equal to the final kinetic energy of the body. We can determine an equation that relates the frictional force to the initial speed of the carriage, so we will determine the coefficient of friction.

\frac{1}{2} *m*v_{i}^{2}-(F*d)=  \frac{1}{2} *m*v_{f}^{2}

where:

vf = final velocity = 0

vi = initial velocity = 85 [km/h] = 23.61 [m/s]

d = displacement = 900 [m]

F = friction force [N]

The final velocity is zero since when the vehicle has traveled 900 meters its velocity is zero.

Now replacing:

(1/2)*m*(23.61)^2 = μ*m*g*d

0.5*(23.61)^2 = μ*9,81*900

μ = 0.0315

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Tamiku [17]

Answer: Lightning is mostly light and electricity, this light that is hitting is going at a rate of 299,792.458 km per second (or 186,282 miles per second) this is so much compared to sound which only travels at about 761 mph (or approximately 332 meters per second). Fun fact: The lightening you are seeing is that coming back to the cloud because the process happens so fast.

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2 years ago
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A scientist measures the growth of a bamboo plant over time. The table above shows the results. What is the best interference fo
lisabon 2012 [21]

(B) 2.25cm

<u>Explanation:</u>

Given:

At 40 hours, the height of the bamboo plant is 2.1cm

At 50 hours, the height of the bamboo plant is 2.4cm

Height of the bamboo plant after 45 hours = ?

The difference in length from 40 to 50 hours = 2.4 - 2.1cm

                                                                      = 0.3 cm

Mean of 40 and 50 is 45.

Thus,

At 45 hours, the height will increase by 0.3/2

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Height at 45 hour = 2.1 + 0.15cm

                           = 2.25cm

Therefore, the height of the plant after 45 hours is 2.25cm

7 0
3 years ago
Calculate the average speed in metres per second from Glasgow to Edinburgh
mariarad [96]
This is the same question as the one previously but with more details, so I will just use my previous answer.

1800 to 1820 is 20 minutes.1830 to 1838 is 8 minutes.1840 to 1905 is 25 minutes.
The total time travelled is 20+8+25 = 53 minutes = 3180 seconds.
The distance between Glasgow and Edinburgh is 28 + 12 + 34 = 74 km = 74000 m.

So, the average speed is 74000m/3180s = 23.27 m/s (4 s.f.)
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2 years ago
a person throws a ball upward into the air with an initial velocity of 20 m/s. calculate (a) how high it goes, and (b) how long
Phantasy [73]

Answer:

a) about 20.4 meters high

b) about 4.08 seconds

Explanation:

Part a)

To find the maximum height the ball reaches under the action of gravity (g = 9.8 m/s^2) use the equation that connects change in velocity over time with acceleration.

a=\frac{Vf-Vi}{t}

-9.8 \frac{m}{s} =\frac{Vf-Vi}{t}

In our case, the initial velocity of the ball as it leaves the hands of the person is Vi = 20 m/s, while thw final velocity of the ball as it reaches its maximum height is zero (0) m/s. Therefore we can solve for the time it takes the ball to reach the top:

-9.8  =\frac{0-20}{t}\\t=\frac{20}{9.8} s = 2.04 s

Now we use this time in the expression for the distance covered (final position Xf minus initial position Xi) under acceleration:

Xf-Xi=Vi*t+\frac{1}{2} a t^{2} \\Xf-Xi=20*(2.04)-\frac{1}{2} 9.8*2.04^{2}\\Xf-Xi=20.408 m

Part b) Now we use the expression for distance covered under acceleration to find the time it takes for the ball to leave the person's hand and come back to it (notice that Xf-Xi in this case will be zero - same final and initial position)

Xf-Xi=0=20*(t)-\frac{1}{2} 9.8*t^{2

To solve for "t" in this quadratic equation, we can factor it out as shown:

0= t(20-\frac{9.8}{2} t)

Therefore there are two possible solutions when each of the two factors equals zero:

1) t= 0 (which is not representative of our case) , and

2) the expression in parenthesis is zero:

0= 20-\frac{9.8}{2} t\\t=\frac{20*2}{9.8} = 4.08 s

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3 years ago
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Answer:A

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The molecules that makes up solids are held together by bonds. When heat is added,the molecules begin to move as a result,the bonds break and it turns to liquid.this process is called melting. The reverse of melting is freezing.

Liquid are made up of molecules that moves more freely than solids. When heat is added to liquid,the molecules gain more energy and begins to move faster. This causes them to turn to gases.

This process is called evaporation. It occurs at different temperature for different substances.

The particles of gases move more faster and are separated by large distances. A gas can change back to a liquid through condensation.

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