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mihalych1998 [28]
3 years ago
9

Un auto de 1000 kg que lleva una velocidad de 72 km/h se detiene en una distancia de 100 metros cuando se le aplican los frenos.

(a) ¿Cuál es la fuerza constante producida por los fre. Nos? (b) Con esta fuerza, ¿cuál seria la distancia de frena do si la velocidad hubiera sido de 36 km/h?
Physics
1 answer:
Flura [38]3 years ago
6 0

Answer:

a)    F = 2000 N , B)   x = 25 m

Explanation:

a) To solve this exercise we can use the relationship between work and kinetic energy

          W = ΔK

The job is

           W = -F x

the negative sign is because the force of the brakes is contrary to the movement

as the car stops its final kinetic energy is zero

           K = ½ m v²

let's substitute

         - F x = 0 - ½ m v²

            F = ½ m v² / x

Let's reduce the magnitudes to the SI system

           v = 72 km / h (1000m / 1km) (1 h / 3600 s) = 20 m / s

let's calculate

          F = ½ 1000 20²/100

          F = 2000 N

b) x = ½ mv2 / F

let's slow down to the SI system

         v = 36 km / h = 10 m / s

let's calculate

             x = ½ 1000 10²/2000

             x = 25 m

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Answer:

C

Explanation:

The electric field inside a conductor is always zero if the charges inside the conductor are not moving.

Since the electron are not moving then they must be in electrostatic equilibrium which means the electric field inside the conductor is zero. if the electric field existed inside the conductor then there will be net force on all the electrons and the electrons will accelerate.

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According to the condensation theory, the most important factor for the formation of our planets was _____. the gravitational pu
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5 0
3 years ago
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a 5.5 g dart is fired into a block of wood with a mass of 22.6 g. the wood block is initially at rest on a 1.5 m tall post. afte
IgorLugansk [536]
<span>From the problem alone we can say that the dart and the block of wood combined into a single object moving together at the end. With that clue we know that the collision is an inelastic collision. The formula of an inelastic collision is:

m_{1}v_{1i}+m_{2}v_{2i}=(m_{1}+m_{2})v_{f}

First let us sort out our given:Mass should be in kg to get the proper answer. Now let's assign m1 as the mass of the dart and m2 as the mass of the block. 
m1 = 5.5g

5.5g x \frac{1kg}{1000g}= 0.0055kg

m2 = 22.6g

22.6g x \frac{1kg}{1000g}= 0.0226kg

So now we settled that we can set our given as:
M1 = .0055 kg
v1i = ?
M2 = 0.0226 kg
v2i = 0 m/s
dx = 2.5 m
dy = -1.5 m

Now you can see that we have 2 unknowns: v1i and vf. We need the vf to solve for the initial velocity of the dart or object 1. We have other given to consider, so we can make use of that to get our missing vf. 

Now, vf is the horizontal velocity after the collision. We do this by first using the equations for projectiles considering that we have an x and y dimension to consider. We use the y dimension to get the x. 
</span>

dy = -1.5 m 

a = 9.8m/s^2

viy = 0 (take note that the initial vertical velocity is 0)

t = ?

<span>We can use the UAM equations to solve for the time in the y-dimension (vertical) to get the horizontal velocity. 

dy = v_{iy}t +  \frac{1}{2} at^{2}</span>

1.5 = (0)t+\frac{1}{2} (9.8)t^{2}

<span>1.5 = \frac{1}{2} (9.8)t^{2}

\frac{(2)(1.5)}{9.8}=t^{2}

\frac{(3)}{9.8}=t^{2}

\sqrt{0.3061} = \sqrt{t^{2}

0.553s = t

Now using this, we can get the horizontal (x-dimension) velocity using the formula:
v_{x} =d_{x}t and our given earlier for the horizontal distance is 2.5m and we solved for time 0.553s. Let's put that into our equation:
v_{x} =d_{x}t
v_{x} =(2.5m)(0.553s) 
v_{x} =4.52m/s

Now we finally have our vf or velocity after the collision. Now let's get back to the equation.

m_{1}v_{1i}+m_{2}v_{2i}=(m_{1}+m_{2})v_{f}

From this we can derive the equation for v1i by isolating it. 

v_{1i}= \frac{((m_{1}+m_{2})v_{f})-(m_{2}v_{2i})}{m_{1}}

Now let's put in all our given and what we solved:

v_{1i}= \frac{((0.0055kg+0.0226kg)4.52m/s)-((0.0226kg)0m/s)}{0.0055kg}

v_{1i}= \frac{(0.0281kg)4.52m/s)}{0.0055kg}

v_{1i}= \frac{0.127012kg.m/s}{0.0055kg}

v_{1i}= 23.09m/s

The initial speed of the dart is 23.09 m/s or 23.10 m/s.</span>
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4 years ago
g An astronaut must journey to a distant planet, which is 189 light-years from Earth. What speed will be necessary if the astron
Butoxors [25]

Answer:

The value is v  =  2.999 *10^{8} \  m/s

Explanation:

From the question we are told that

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    The  time to be spent on the ship is  t_{s} =  12 \  years

Generally speed can be obtained using the mathematical relation represented below

       t_s  =  2 * t *  \sqrt{1 -  \frac{v^2}{c^2 } }

The 2 in the equation show that the trip is a round trip i.e going and coming back

=>    12 =  2 * 189 *  \sqrt{1 -  \frac{v^2}{(3.0*10^{8})^2 } }

=>     v  =  2.999 *10^{8} \  m/s

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Assuming it's an ideal material, the answer is A.

The speed of sound depends on the medium that the sound travels through.
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