Answer:
<em>1.228 x </em><em> mm </em>
<em></em>
Explanation:
diameter of aluminium bar D = 40 mm
diameter of hole d = 30 mm
compressive Load F = 180 kN = 180 x N
modulus of elasticity E = 85 GN/m^2 = 85 x Pa
length of bar L = 600 mm
length of hole = 100 mm
true length of bar = 600 - 100 = 500 mm
area of the bar A = =
= 1256.8 mm^2
area of hole a = =
= 549.85 mm^2
Total contraction of the bar =
total contraction =
==> = <em>1.228 x </em>
<em> mm </em>
Answer:
a) 17.16m/s
b) 44,145J
c) Sound the piano makes when hitting the ground, vibration of the ground, heat.
d) i) It's smaller due to the energy dissipated by the friction between air and the parachute.
ii) It stays the same, the only difference is that the dissipated energy is distributed between air resistance and the kinetic energy dissipated by the ground whent he piano hits it.
Explanation:
a)
In order to solve this problem we must start by doing a drawing of the situation, which will help us visualize the problem better. (See attached picture).
So, in this problem we can ignore air resistance so we can say that the energy is conserved, this is the total initial energy is the same as the total final energy, so we get that:
When the piano is released it has an initial speed of zero, so the initial kinetic energy is zero. When the piano hits the ground it will have a height of 0m, so the final potential energy is zero as well. This will simplify our equation:
We know that potential energy is given by the formula:
U=mgh
and kinetic energy is given by the formula:
which can be substituted in our equation:
we can divide both sides of the equation into the mass of the piano, so we get:
which can be solved for the final velocity which yields:
we can now substitute the data provided by the problem so we get:
which yields:
v=17.16m/s
b)
Since energy is conserved, this means that the total dissipated energy will be the same as the potential energy, so we get that:
E=mgh
so
which yields:
E=44,145J
c)
When the piano hits the ground, the kinetic energy it had will be transformed to other types of energy, mostly vibration and heat. The vibration will turn to sound due to the movement of air created by the piano itself and the ground. And heat is created by the friction between the molecules created by the vibrations and the collition itself. So some of the indicators of this release of energy could be:
-Sound
-Vibration
-Heat.
d)
i) The amount of inetic energy dissipated would decrease due to the friction between air and the parachute. Since air is resisting the movement of the piano, this will translate into a loss of energy, if we did an energy balance we would get that:
The total amount of energy is conserved but it will be distributed between the energy lost due to air resistance and the kinetic energy the piano has at the time it hits the ground.
ii) So the total amount of energy dissipated remains the same, the only difference is that it will be distributed between air resistance and the kinetic energy of the piano.
