Answer:
The girl is doing work on the ball because the energy in her muscles changed, even though the ball is not displaced.
Explanation:
The complete question is...
Which of these correctly describes whether a girl holding a ball in the same position is doing work on the ball?
-The girl is doing work on the ball because the energy of the ball changed, even though it is not displaced.
-The girl is doing work on the ball because the energy in her muscles changed, even though the ball is not displaced.
-The girl is doing no work on the ball because the ball is not displaced.
-The girl is doing no work on the ball because she is exerting a net force on the ball.
Holding up a ball costs energy, which is used to counter the work that would have otherwise be done on the ball by gravity. Although no physical distance is moved, we should consider the fact that by holding the ball, the girls hand exerts physical force to hold the ball in place. Also, there is a potential gravitational work on the ball due to gravity, but the force exerted by the girls hand does an equivalent of this gravito-potential work in order to counter it and hold the ball in place. All these activities eventually lead to a change in energy in her hand muscle to show that energy is expended.
The pressure is 5000 Pa
Explanation:
The pressure exerted by a force on a surface is given by the equation:
where
p is the pressure (measured in Pascal, Pa)
F is the magnitude of the force
A is the area of the surface on which the force is exerted
In this problem, we have:
F = 2 N
Substituting into the equation, we find the pressure:
Learn more about pressure:
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Answer:
The height of a tower would be 27.5 meters
Explanation:
Notice that in both cases you are dealing with diagrams representing vertical objects and shadows created by the sun, against the ground, so we are in the presence of right angle triangles which have in common another angle (that made by the rays of the sun. So we can use similar triangles and the proportion that is generated based on the quotient of similar sides to find the unknown height (h).
Answer:
F = 30 N Directed up
Explanation:
We can solve this problem using the momentum and momentum relationship.
I = ΔP
I = ∫ F dt
As we are asked for the average force, that leaves the integral, giving
I = F t
F t = m - m v₀
F = m (-v₀) / t
Note that, if you define the upward positive direction, the initial velocity is negative
Let's calculate
F = 0.15 (3.5 - (-6.5)) / 0.050
F = 30 N
Directed up
Answer: D) 3.2 × 10^8
Explanation: Insulators are best described as materials which are poor conductors of electricity and hence do not allow passage of electricity through them. Resistivity are hence used to describe property or characteristic of a material which does not allow the flow or passage of electric current.
In summary, materials which high resistivity values are referred to as Insulators. Conversely, those with low resistivity or high conductivity values are called conductors while those with intermediate values are named semiconductors.
In the question given above, the material with a resistivity value of 3.2 × 10^8 - - - has a very high resistivity value (320000000Ω), the other options given have very low resistivity values ; 0.0000000017, etc and are most likely to be conductors due to their excessively low resistivity values.