. An archer using a simple bow exerts a force of 180 N to draw back the bow string 0.50 m. (a) What is the average work done by the archer in preparing to launch her arrow? (Hint: Compute the average work as you would any average quantity: average work = [final work - initial work].) (b) If all the work is converted into the kinetic energy of the arrow upon its release, what is the arrow's speed as it leaves the bow? Assume the mass of the arrow is 0.021 kg and ignore any kinetic energy in the bow as it relaxes to its original shape. (c) If the arrow is shot straight up, what is the maximum height achieved by the arrow? Ignore any effects due to air resistance in making your assessment.
. An archer using a simple bow exerts a force of 180 N to draw back the bow string 0.50 m. (a) What is the average work done by the archer in preparing to launch her arrow? (Hint: Compute the average work as you would any average quantity: average work = [final work - initial work].) (b) If all the work is converted into the kinetic energy of the arrow upon its release, what is the arrow's speed as it leaves the bow? Assume the mass of the arrow is 0.021 kg and ignore any kinetic energy in the bow as it relaxes to its original shape. (c) If the arrow is shot straight up, what is the maximum height achieved by the arrow? Ignore any effects due to air resistance in making your assessment.
Solution Summary: The author concludes that the average work done by archer is 45J. The kinetic energy of an object is given as KE=12mv2.
. An archer using a simple bow exerts a force of 180 N to draw back the bow string 0.50 m. (a) What is the average work done by the archer in preparing to launch her arrow? (Hint: Compute the average work as you would any average quantity: average work = [final work - initial work].) (b) If all the work is converted into the kinetic energy of the arrow upon its release, what is the arrow's speed as it leaves the bow? Assume the mass of the arrow is 0.021 kg and ignore any kinetic energy in the bow as it relaxes to its original shape. (c) If the arrow is shot straight up, what is the maximum height achieved by the arrow? Ignore any effects due to air resistance in making your assessment.
ROTATIONAL DYNAMICS
Question 01
A solid circular cylinder and a solid spherical ball of the same mass and radius are rolling
together down the same inclined. Calculate the ratio of their kinetic energy. Assume pure
rolling motion Question 02
A sphere and cylinder of the same mass and radius start from ret at the same point and more
down the same plane inclined at 30° to the horizontal
Which body gets the bottom first and what is its acceleration
b) What angle of inclination of the plane is needed to give the slower body the same
acceleration
Question 03
i)
Define the angular velocity of a rotating body and give its SI unit
A car wheel has its angular velocity changing from 2rads to 30 rads
seconds. If the radius of the wheel is 400mm. calculate
ii)
The angular acceleration
iii)
The tangential linear acceleration of a point on the rim of the wheel
Question 04
in 20
Question B3
Consider the following FLRW spacetime:
t2
ds² = -dt² +
(dx²
+ dy²+ dz²),
t2
where t is a constant.
a)
State whether this universe is spatially open, closed or flat.
[2 marks]
b) Determine the Hubble factor H(t), and represent it in a (roughly drawn) plot as a function
of time t, starting at t = 0.
[3 marks]
c) Taking galaxy A to be located at (x, y, z) = (0,0,0), determine the proper distance to galaxy
B located at (x, y, z) = (L, 0, 0). Determine the recessional velocity of galaxy B with respect
to galaxy A.
d) The Friedmann equations are
2
k
8πG
а
4πG
+
a²
(p+3p).
3
a
3
[5 marks]
Use these equations to determine the energy density p(t) and the pressure p(t) for the
FLRW spacetime specified at the top of the page.
[5 marks]
e) Given the result of question B3.d, state whether the FLRW universe in question is (i)
radiation-dominated, (ii) matter-dominated, (iii) cosmological-constant-dominated, or (iv)
none of the previous. Justify your answer.
f)
[5 marks]
A conformally…
SECTION B
Answer ONLY TWO questions in Section B
[Expect to use one single-sided A4 page for each Section-B sub question.]
Question B1
Consider the line element
where w is a constant.
ds²=-dt²+e2wt dx²,
a) Determine the components of the metric and of the inverse metric.
[2 marks]
b) Determine the Christoffel symbols. [See the Appendix of this document.]
[10 marks]
c)
Write down the geodesic equations.
[5 marks]
d) Show that e2wt it is a constant of geodesic motion.
[4 marks]
e)
Solve the geodesic equations for null geodesics.
[4 marks]
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