Estimate the acceleration you subject yourself to if you walk into a brick wall at normal walking speed. (Make a reasonable esti
1 answer:
Answer:
From certain assumptions that the walking speed is 2 m/s, and the stop time is 0.1 s the acceleration would be -20 m/s
Explanation:
Using the average acceleration formula:
where
and
are the changes in the speed and time respectively.
We have by assuming that the walking speed is 2 m/s and the stop time is 0.1s which is equal to the change in time during the stopping.
, where
are the initial speed and final speed respectively, and
Plugging the previous in the average acceleration formula we get
where the minus sign indicates an acceleration in the opposite direction of the motion (or in other word opposite to the speed's direction).
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Answer:
a) ΔEC=-23.4kW
b)W=12106.2kW
c)
Explanation:
A)
The kinetic energy is defined as:
(vel is the velocity, to differentiate with v, specific volume).
The kinetic energy change will be: Δ ()=
Δ ()=
Where 1 and 2 subscripts mean initial and final state respectively.
Δ()=
This amount is negative because the steam is losing that energy.
B)
Consider the energy balance, with a neglective height difference: The energy that enters to the turbine (which is in the steam) is the same that goes out (which is in the steam and in the work done).
We already know the last quantity: =
Δ (
)=23400W
For the steam enthalpies, review the steam tables (I attach the ones that I used); according to that,
The exit state is a liquid-vapor mixture, so its enthalpy is:
Finally, the work can be obtained:
C) For the area, consider the equation of mass flow:
where
is the density, and A the area. The density is the inverse of the specific volume, so
The specific volume of the inlet steam can be read also from the steam tables, and its value is: , so:
1) Initial upward acceleration:
2) Mass of burned fuel:
Explanation:
1)
There are two forces acting on the rocket at the beginning:
- The force of gravity, of magnitude , in the downward direction, where
is the rocket's mass
is the acceleration of gravity
- The thrust of the motor, T, in the upward direction, of magnitude
According to Newton's second law of motion, the net force on the rocket must be equal to the product between its mass and its acceleration, so we can write:
(1)
where a is the acceleration of the rocket.
Solving for a, we find the initial acceleration:
2)
When the rocket reaches an altitude of 5000 m, its acceleration has increased to
The reason for this increase is that the mass of the rocket has decreased, because the rocket has burned some fuel.
We can therefore rewrite eq.(1) as
where
is the new mass of the rocket
Re-arranging the equation and solving for m', we find
And since the initial mass of the rocket was
This means that the mass of fuel burned is