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Anuta_ua [19.1K]
2 years ago
9

A rope exerts a force F on a 20.0-kg crate. The crate starts from rest and accelerates upward at 5.00 m/s2 near the surface of t

he earth. What is the kinetic energy (in J) of the crate when it is 4.0 m above the floor?
Physics
1 answer:
tia_tia [17]2 years ago
5 0

Answer:

400 J

Explanation:

Given:

Δy = 4.00 m

v₀ = 0 m/s

a = 5.00 m/s²

Find: v²

v² = v₀² + 2aΔy

v² = (0 m/s)² + 2 (5.00 m/s²) (4.00 m)

v² = 40.0 m²/s²

Find KE:

KE = ½ mv²

KE = ½ (20.0 kg) (40.0 m²/s²)

KE = 400 J

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What is the volume of an irregularly shaped object that has a mass 3.0 grams and a density of 6.0 g/mL
pogonyaev

Answer: The volume of an irregularly shaped object is 0.50 ml

Explanation:

To calculate the volume, we use the equation:

\text{Density of substance}=\frac{\text{Mass of substance}}{\text{Volume of substance}}

Density of object = 6.0g/ml

mass of object = 3.0 g

Volume of object = ?

Putting in the values we get:

6.0g/ml=\frac{3.0g}{\text{Volume of substance}}

{\text{Volume of substance}}=0.50ml

Thus the volume of an irregularly shaped object is 0.50 ml

4 0
2 years ago
Explain why the brakes of a car get much hotter than the brakes of a bicycle?
ValentinkaMS [17]

Answer: Car brakes produces more energy then the bicycle because the cars wheels produces a much bigger force that makes the car go and to stop that force the car uses greater amount of energy that transfers to heat  but in a bicycle the wheels do not turn that fast so when you press the break there is less energy that transfer to heat.

Explanation:

8 0
2 years ago
Imagine that the satellite described in the problem introduction is used to transmit television signals. You have a satellite TV
Korolek [52]

Complete Question

A satellite in geostationary orbit is used to transmit data via electromagnetic radiation. The satellite is at a height of 35,000 km above the surface of the earth, and we assume it has an isotropic power output of 1 kW (although, in practice, satellite antennas transmit signals that are less powerful but more directional).

Imagine that the satellite described in the problem introduction is used to transmit television signals. You have a satellite TV reciever consisting of a circular dish of radius R which focuses the electromagnetic energy incident from the satellite onto a receiver which has a surface area of 5 cm2.

How large does the radius R of the dish have to be to achieve an electric field vector amplitude of 0.1 mV/m at the receiver?

For simplicity, assume that your house is located directly beneath the satellite (i.e. the situation you calculated in the first part), that the dish reflects all of the incident signal onto the receiver, and that there are no losses associated with the reception process. The dish has a curvature, but the radius R refers to the projection of the dish into the plane perpendicular to the direction of the incoming signal.

Give your answer in centimeters, to two significant figures.

Answer:

 The radius  of  the dish is R = 18cm

Explanation:

  From the question we are told that

     The radius of the orbit is  = R = 35,000km = 35,000 *10^3 m

    The power output of the power is  P = 1 kW = 1000W

   The electric vector amplitude is given as E = 0.1 mV/m = 0.1 *10^{-3}V/m

    The area of thereciever  is   A_R = 5cm^2

Generally the intensity of the dish is mathematically represented as

         I = \frac{P}{A}

Where A is the area orbit which is a sphere so this is obtained as

          A = 4 \pi r^2

              = (4 * 3.142 * (35,000 *10^3)^2)

              =1.5395*10^{16} m^2

  Then substituting into the equation for intensity

          I_s  =  \frac{1000}{1.5395*10^{16}}

            = 6.5*10^ {-14}W/m2

 Now the intensity received by the dish can be mathematically evaluated as

              I_d = \frac{1}{2}  * c \epsilon_o E_D ^2

  Where c is thesped of light with a constant value  c = 3.0*10^8 m/s

              \epsilon_o is the permitivity of free space  with a value  8.85*10^{-12} N/m

              E_D is the electric filed on the dish

So  since we are to assume to loss then the intensity of the satellite is equal to the intensity incident on the receiver dish

      Now making the eletric field intensity the subject of the formula

                  E_D = \sqrt{\frac{2 * I_d}{c * \epsilon_o} }

substituting values

                 E_D = \sqrt{\frac{2 * 6.5*10^{-14}}{3.0*10^{8} * 8.85*10^{-12}} }

                       = 7*10^{-6} V/m

The incident power on the dish is what is been reflected to the receiver

                P_D = P_R

Where P_D is the power incident on the dish which is mathematically represented as

              P_D = I_d A_d

                   = \frac{1}{2}  c \epsilon_o E_D^2  (\pi R^2)

And  P_R is the power incident on the dish which is mathematically represented as

                 P_R = I_R A_R

                       = \frac{1}{2} c \epsilon_o E_R^2 A_R

Now equating the two

                \frac{1}{2}  c \epsilon_o E_D^2  (\pi R^2) =  \frac{1}{2} c \epsilon_o E_R^2 A_R

   Making R the subject we have

                   R = \sqrt{\frac{E_R^2 A_R}{\pi E_D^2} }

Substituting values

                   R = \sqrt{\frac{(0.1 *10^{-3})^2 * 5}{\pi (7*10^{-6})^ 2} }

                     R = 18cm

8 0
2 years ago
A disk is spinning about its center with a constant angular speed at first. Let the turntable spin faster and faster, with const
hoa [83]

Answer:

4 (please see the attached file)

Explanation:

While the angular speed (counterclockwise) remained constant, the angular acceleration was just zero.

So, the only force acting on the bug (parallel to the surface) was the centripetal force, producing a centripetal acceleration directed towards the center of the disk.

When the turntable started to spin faster and faster, this caused a change in the angular speed, represented by the appearance of an angular acceleration α.

This acceleration is related with the tangential acceleration, by this expression:

at = α*r

This acceleration, tangent to the disk (aiming in the same direction of the movement, which is counterclockwise, as showed in the pictures) adds vectorially with the centripetal force, giving a resultant like the one showed in the sketch Nº 4.

7 0
2 years ago
Two very large, flat plates are parallel to each other. Plate A, located at y=1.0 cm, is along the xz-plane and carries a unifor
Dmitry [639]

Answer:

 E ≈ 1.70 10⁵ N/C

Explanation:

The electric field is a vector quantity, so we can calculate the field of each plate and then add them. To calculate the field of a plate let's use Gauss's law

       Φ = ∫ E. dA = q_{int} / ε₀

To apply this law we must create a Gaussian surface that takes advantage of the symmetry of the problem. The electric field lines on the surface are perpendicular, so the Gaussian surface that will be a cylinder with the base parallel to the plate.

On this surface the normal to the base (A) is parallel to the field lines whereby the scalar product is reduced to the ordinary product. The normal on the sides of the cylinder is perpendicular to the field, therefore, the product scale is zero.

        ∫I E dA = q_{int}  /ε₀

Let's look for the load under the cylinder, let's use the concept of load density

        σ =  q_{int} / A

         q_{int} = σ A

Let's write Gauss's law for this case

       E A =  q_{int} /ε₀  

       E A = σ A / ε₀

       E = σ / ε₀

As the field is emitted for each side of the plate the value to only one side is

      E = G / 2ε₀  

This expression is the same for each plate, now let's add the electric field at the requested point

     R = (0.50, 0.00, 0.00) cm

We see that this point is on the X axis, between the plates that are at the points y = -1.0 cm and y = 1.0 cm, as the plates are very large the test point is between them

The negative plate has an incoming field and the positive plate has an outgoing field, the test load is always positive. The field due to the negative plate goes to the left, the field through the positive plate goes to the left at this point whereby two are added

     E = E_ + E +

     E = σ1 / 2ε₀  + σ2 / 2ε₀  

     E = 1 / 2o (σ1 + σ2)

Let's calculate the value

     E = 1/2 8.85 10⁻¹² (1.00 10⁻⁶ + 2.00 10⁻⁶)

     E = 3 10⁻⁶ / 17.7 10⁻¹²

     E = 1,695 10⁵ N / C

     E ≈ 1.70 10⁵ N/C

6 0
2 years ago
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