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Kruka [31]
3 years ago
12

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 stay

s 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?
Physics
1 answer:
yuradex [85]3 years ago
4 0

Answer:

5.71428571422 m/s

Explanation:

u = Initial velocity = 20 m/s

v = Final velocity

s = Displacement

a = Acceleration

Time taken = 15-1 = 14 s

Distance traveled in 1 second = 20\times 1=20\ m

s=ut+\frac{1}{2}at^2\\\Rightarrow 200-20=20\times 14+\frac{1}{2}\times a\times 14^2\\\Rightarrow a=\frac{2(180-20\times14)}{14^2}\\\Rightarrow a=-1.02040816327\ m/s^2

v=u+at\\\Rightarrow v=20-1.02040816327\times 14\\\Rightarrow v=5.71428571422\ m/s

The speed as she reaches the light at the instant it turns green is 5.71428571422 m/s

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A power plant produces 1000 MW to suply a city 40Km away.Current flows from the power plant on a single wire of resistance0.050
Westkost [7]

Answer:

The current in wire resistance 2Ω

a). 8696 A

b). fraction power 15.1% a 115kV

Explanation:

Resistance

R=0.05Ω/Km*40km

R=2Ω

P=1000 MW

a).

P=V*I\\I=\frac{P}{V}=\frac{1000x10^{6}W}{115x10^{3}k }  =8696.65A

Using law ohm

b).

V=I*R\\I=\frac{V}{R}

P=I*I*R\\P=I^{2} *R\\P=8696.65^{2}*2\\P=151.228 x10^{6}  W

e=\frac{151.228x10^{6} }{1000x10^{6} }*100= 15.12%

8 0
3 years ago
1. Tectonic plates that move toward each other ...A Mantle
KATRIN_1 [288]

Answer:

Its convergent

Explanation:

There areas where plates move toward each other and collide Also known as compressional pr destructive boundaries.

5 0
3 years ago
The redshift of a star means that _____.
Gelneren [198K]
The correct answer is D. the star is getting farther away.

When the light has red-shifted, it shows that everything is moving away from a certain point. This is known as the Doppler effect and proves the Big Bang (which would be the center point that everything is moving away from). Just as a 'for your information', blue shift is when the star is moving towards us.

Hope I helped :)
4 0
3 years ago
Read 2 more answers
If E=1/2Av^2+Bmx find the dimensions of A and B(Where E is energy,v,m and x are velocity,mass and distance respectively)
sp2606 [1]

Answer:

A = [kg]

B = [m/s²]

Explanation:

E = ½ Av² + Bmx

Substitute the units:

[J] = ½ A [m/s]² + B [kg] [m]

A Joule written in base units is:

1 J = 1 Nm = 1 kg m²/s²

Each term must have the same units.

[kg m²/s²] = A [m/s]²

[kg m²/s²] = A [m²/s²]

A = [kg]

[kg m²/s²] = B [kg] [m]

B = [m/s²]

8 0
3 years ago
A 10,000-kg railroad car travels down the track at 30 m/s and hits a second stationary railroad car of 20,000 kg. The cars becom
Ivanshal [37]

Answer:

10 m/s

Explanation:

The problem can be solved by using the law of conservation of momentum: the initial momentum has to be equal to the final momentum, so we can write the following

p_i = p_f

m_1 u_1 + m_2 u_2 = (m_1 +m_2 )v

where

m_1 = 10,000 kg is the mass of the first car

u_1=30 m/s is the initial velocity of the first car

m_2 = 20,000 kg is the mass of the second car

u_2 = 0 is the initial velocity of the second car

v is the final velocity of the two combined cars after the collision

Re-arranging the equation and substituting the numbers, we find

v=\frac{m_1 u_1 +m_2 u_2}{m_1+m_2}=\frac{(10,000)(30)-0}{10,000+20,000}=10 m/s


6 0
3 years ago
Read 2 more answers
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