UNIVERSITY OF SOUTHERN DENMARK
Sønderborg
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The Faculty of Engineering
MECH1
Semester 1 MC+EIB+ME
EXAMINATION
Wednesday 6 January 2021 at 9:00 – 12:00
Exam aids:
Everything.
Internet is only allowed to access the materials on itslearning
and for uploading your solutions.
Any kind of communication is strictly forbidden.
Enclosures:
None.
Note:
Please make sure that you write down every step of the way you solve the exercises, not only the
final solution – the points are awarded for each of the steps!
Final solutions alone will not be recognized as sufficient for getting any points.
Question 1 starts on page 2
MECH1, Examination – January 2022
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Question 1
The figure below shows the unit cell of boron arsenide.
Boron and arsenic atoms are colored in pink and purple, respectively.
(a) How many boron and arsenic atoms, respectively, are there in the unit cell?
(b) Does boron arsenide have a close-packing structure?
Question 2
A 2 m copper wire with a square cross-section of 1 mm by 1 mm stretches 1.51 mm
when supporting a 10 kg mass. Suppose you cut a length of 0.2 m of this wire and
hang a 10 kg mass from it. How much will this shore wire stretch?
Question 3
The figure below shows a parallel-plate capacitor. You are not allowed to change the
spacing between the two plates, the area of the plates, or the applied voltage.
(a) What can you do to increase the capacitance?
(b) Explain the mechanism behind the increase of the capacitance.
MECH1, Examination – January 2022
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Question 4
The figure below shows the p-n junction of a light-emitting diode (LED).
This LED has a knee voltage of 3 V, and you have three batteries, i.e. Battery A of
1.5 V, Battery B of 3.1 V, and Battery C of 15 V.
(a) Which battery can be used to make the LED emit light? Schematically draw the
circuit where the battery is connected to the LED.
(b) The LED emits light with a wavelength of 414 nm. What is the energy of the
light?
Question 5 (Statics)
Determine the magnitude P of the vertical force required to lift the
wheelbarrow free of the ground at point B. The combined mass of the
wheelbarrow and its load is 110 kg with centre of mass at G.
500
400
700
800
300
MECH1, Examination – January 2022
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Question 6 (Statics)
Calculate the forces in members AB, AE and DB of the loaded truss.
Question 7 (Statics)
Calculate the reactions at A and B and draw the shear and
moment diagrams for the loaded beam. Determine the values of
the shear force and bending moment at x = 7m distance from A.
8
6
9
9