Phys101
Term:122
Online HW-Ch12-Lec01
Q1:
For an object in equilibrium the net torque acting on it vanishes only if each torque is
calculated about:
A.
B.
C.
D.
E.
the center of mass
the center of gravity
the geometrical center
the point of application of the force
the same point
Ans:
E ; All torques should be calculated about exactly one point.
Q2:
Three identical uniform rods are each acted on by two or more forces, all
perpendicular to the rods and all equal in magnitude. Which of the rods could be in
static equilibrium if an additional force (not shown in the drawing) is applied at
the center of mass of the rod?
A.
B.
C.
D.
E.
Only 1
Only 2
Only 3
Only 1 and 2
All three
x
Ans:
C ; because 1 and 2 will never be in static equilibrium since the forces at the edges
create non-zero net torque.
Q3:
A uniform plank weight equals 120 N and of 3 m length. The support at Y provides a
force of 50 N, while the support at X provides a force of 40 N. The support at Z is
0.75 m far from X. Find the supporting force (in N) at Z if this plank is at
translational equilibrium. (Give your answer in three significant figures form)
40 N
F
50 N
y
𝐀𝐧𝐬:
120 N
Fnet,y = 0 ⇒ F + 40 + 50 − 120 = 0 ⇒ F = 30.0 N
KFUPM-Physics Department
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