A 740 N physics student stands on a bathroom scale in an 850-kg (including the s
ID: 1280548 • Letter: A
Question
A 740 N physics student stands on a bathroom scale in an 850-kg (including the student) elevator that is supported by a cable. As the elevator starts moving, the scale reads 640 N.
(a) Find the acceleration of the elevator (magnitude and direction -- take up to be the positive direction).
(b) What is the acceleration if the scale reads 860 N?
(c) If the scale reads zero, what is the acceleration of the elevator?
(d) What is the tension in the cable in parts (a) and (c)?
cable tension in part (a) 5 =? N cable tension in part (c) 6= NExplanation / Answer
a)640=740+ma
ma=-100N
m=740/g=75.51kg
a=-1.32m/s2
i.e1.32m/s2 downwards
b)860=740+ma
ma=120
a=1.589m/s2 upwards
c)0=740+ma
a=-g=-9.8m/s2
a=9.8m/s2 downwards
i.e it is in free fall
d)T=mg+ma
in case a,T=850(g+a)=7208N
in case c,T=850(g-g)=0
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