ENGR 290 Lecture Notes - Lecture 1: Stopwatch, Net Force
12 Feb 2018
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1. i) A: ▪ The telephone shall withstand temperatures up to 60 oC. B: ▪ The telephone shall withstand
temperatures up to 25 oC.
A is better. B is not sufficient: the customer, a telephone user, very often needs their telephone to work
at temperatures above 25 C.
ii) A: ▪ The statue shall have a base area less than 1 m2 to fit the available space.
▪ The statue shall have a mass of at least 200 kg for stability.
▪ The statue shall exert a pressure of no more than 1 kPa on the base area to prevent sinkage.
B: ▪ The statue shall have a base area less than 1 m2 to fit the available space.
▪ The statue shall exert a pressure of no more than 1 kPa on the base area to prevent sinkage.
B is better. A is not consistent: a 200+ kg statue on a base of < 1m2 exerts a minimum of 2 kPa in Earth
gravity, so it is impossible to satisfy all 3 specifications simultaneously. Further, the 200 kg specification
in A is not traceable: mass is not a parameter that indicates stability.
iii) A: ▪ The car shall be as fast as possible.
B: ▪ The car shall have an average speed greater than 40 km/h.
B is better. A is not quantified.
iv) (Your client is a swimming pool supply manufacturer)
A: ▪ The stopwatch (for timing lap-swimming) shall be waterproof to a depth of 10 m.
B: ▪ The stopwatch (for timing lap-swimming) shall be waterproof to a depth of 100 m.
A is better. B is not traceable: swimming pools do not go to depths beyond 10 m, so there is no need to
set the specification to the significantly more challenging depth.
v) A: ▪ The circuit shall use no more than 3W of power.
▪ The circuit shall operate for at least 24 hours continuously.
B: ▪ The circuit shall use no more than 3W of power, and operate for at least 24 hours continuously.
A is better. B is not singular.
vi) A: ▪The rover shall be able to drive over all rocks whose max length dimension is 30 cm. B:
▪ The rover shall be able to drive over spherical rocks up to 30 cm in diameter.
This one is tricky and could be a legitimate source of debate. On the whole, B is probably better. A is not
verifiable: there is no way to positively demonstrate that something can drive over all rocks of a certain
size, so there is no way to determine if or when you’ve met the specification. At least we can test B. That
being said, it could be challenged that perhaps B is not sufficient. Maybe spherical rocks are not
representative of the worst case of what a rover actually has to drive over.
Nobody promised that writing specifications would be easy.
2. Assume your hovercraft for the ENGR290 competition draws 1.2 amps of current when operating /
racing. Following the “Specification Template” provided, generate a specification related to the capacity
of the hovercraft batteries.
3.
Draw free-body diagrams for the listed objects:
a) m1 assuming a smooth surface (i.e. neglect friction)
b) m1 assuming a rough surface (i.e. with friction)
m
1
m
2
m
3
Document Summary
I(cid:895) a: the telepho(cid:374)e shall (cid:449)ithsta(cid:374)d te(cid:373)peratures up to 6(cid:1004) oc. B: the telepho(cid:374)e shall (cid:449)ithsta(cid:374)d temperatures up to 25 oc. B: the statue shall ha(cid:448)e a (cid:271)ase area less tha(cid:374) (cid:1005) (cid:373)2 to fit the available space: the statue shall exert a pressure of no more than 1 kpa on the base area to prevent sinkage. A is not consistent: a 200+ kg statue on a base of < 1m2 exerts a minimum of 2 kpa in earth gravity, so it is impossible to satisfy all 3 specifications simultaneously. Further, the 200 kg specification in a is not traceable: mass is not a parameter that indicates stability. iii(cid:895) a: the (cid:272)ar shall (cid:271)e as fast as possi(cid:271)le. B: the (cid:272)ar shall ha(cid:448)e a(cid:374) a(cid:448)erage speed greater tha(cid:374) (cid:1008)(cid:1004) k(cid:373)/h. A is not quantified: (your client is a swimming pool supply manufacturer) A: the stop(cid:449)at(cid:272)h (cid:894)for ti(cid:373)i(cid:374)g lap-swimming) shall be waterproof to a depth of 10 m.
