The graph in Figure 4.15 shows the position and time for two runners in a race. Who has the faster speed, Robin or Joel? Explain
how to answer this question without doing calculations.
1 answer:
You might be interested in
Answer: 500 Watts
Explanation:
Power is the speed with which work
is done. Its unit is Watts (
), being
.
Power is mathematically expressed as:
(1)
Where is the time during which work
is performed.
On the other hand, the Work done by a Force
refers to the release of potential energy from a body that is moved by the application of that force to overcome a resistance along a path. It is a scalar magnitude, and its unit in the International System of Units is the Joule (like energy). Therefore, 1 Joule is the work done by a force of 1 Newton when moving an object, in the direction of the force, along 1 meter (
).
When the applied force is constant and the direction of the force and the direction of the movement are parallel, the equation to calculate it is:
(2)
In this case, we have the following data:
So, let's calculate the work done by Peter and then find how much power is involved:
From (2):
(3)
(4)
Substituting (4) in (1):
(5)
Finally:
The thermal expansion of the materials allows to find the deflection of the bimetallist strip is Δy = 3.48 cm
given paramers
* Bimetallic brass / steel tape
* Initial temperature, room temperature T = 20ºC
* Final temperature, boiling water = 100ºC
* initial length L₀ = 222mm (1cm / 10mm) = 22.2cm
* thickness of bimetallic tape e = 0.036 inch (2.54 cm/1 inch) = 0.0914 cm
to find
* perpendicular deviation or deflection (Δy)
Thermal expansion is the phenomenon of change in the length of a body due to the change in temperature, due to the increase in the length of the atomic and molecular bonds, macroscopically it is described by
ΔL = α L₀ ΔT
ΔL and ΔT are the variation of the length and temperature respectively, L₀ is the initial length and α the coefficient of expansion ends.
In this case we have a strip formed by two materials with different coefficient of thermal expansion,
Brass α_{brass} = 19 10⁻⁶ ºC⁻¹
Steel α_{steel} = 11 10⁻⁶ ºC⁻¹
In the attached we can see a diagram of the process, as the temperature increases, the material with greater thermal expansion lengthens more, so the system must curve towards the center of the material with less
thermal expansion. Let's find the length of the strip for each material
brass L_{f brass} - L₀ = α_{brass} L₀ ΔT
Steel L_{f steel} - L₀ = \alpha_{steel} L₀ ΔT
Note that the initial length is the same for the two materials and that the strip is in thermal equilibrium at room temperature.
If we assume that we have an arc of circumference, we can write the length of the arc
θ = L / r
where θ is the angle in radines, L the length of the arc and r the radius of curvature, let's write this equation for each material
brass L_{f \ brass} =θ r₁
steel L_{f \ steel} = θ r₂
we substitute in our equations
θ r₁ - L₀ = α_{brass} L₀ ΔT
θ r₂ - L₀ = α_{steel} L₀ ΔT
let's subtract the two equations
θ (r₁- r₂) = L₀ ΔT (α_{brass} - α_{steel})
the thickness of the strip is
e = r₁ -r₂
θ =
we calculate
θ =
θ = 0.155 rad
Let's use trigonometry to find the perpendicular deflection
tan θ = Δy / L₀
Δy = L₀ tan θ
Δy = 22.2 tan 0.155
Δy = 3.48 cm
Using the thematic expansion of the two materials we find the deflection of the bimetallist strip is 3.38 cm
Learn more about thermal expansion here: brainly.com/question/18717902
