Physics 9702 Doubts | Help Page 225
Question 1069: [Matter > Deformation]
The diagram represents a steel tube with wall thickness w which is small
in comparison with the diameter of the tube.
The tube is under tension, caused by a force T, parallel to the axis of
the tube. To reduce the stress in the material of the tube, it is proposed to
thicken the wall.
The tube diameter and the tension being constant, which wall thickness
gives half the stress?
A w / 2 B √2 w C
2w D 4w
Reference: Past Exam Paper – June 2015 Paper 12 Q23
Solution 1069:
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Question 1070: [Dynamics > Collision]
Two equal masses X and Y are moving towards each other on a frictionless
air track as shown. The masses make an elastic collision.
Which row gives possible velocities for the two masses after the
collision?
velocity of X velocity of Y
A zero 20 cm s–1
to the right
B 10 cm s–1 to
the right 10 cm s–1
to the right
C 20 cm s–1 to
the left zero
D 30 cm s–1 to
the left 50 cm s–1
to the right
Reference: Past Exam Paper – June 2008 Paper 1 Q10
Solution 1070:
Answer: D.
For an elastic collision,
Relative speed of approach = Relative speed of separation
Since the masses are moving towards each other initially, they are
‘approaching’.
Relative speed of approach = 50 + 30 = 80 cm s–1
The relative speed of separation should also be 80 cm s–1.
A and C are incorrect since their relative speed is 20 cm s–1.
B is incorrect since the relative speed is zero.
For choice D, mass X is moving to the left while mass Y is moving to the
right – so they are separating.
Relative speed of separation = 30 + 50 = 80 cm s–1
Question 1071: [Pressure]
A rectangular metal bar exerts a pressure of 15 200 Pa on the horizontal
surface on which it rests.
If the height of the metal bar is 80 cm, what is the density of the metal?
A 190 kg m–3 B 1900 kg m–3 C 19 000 kg m–3 D 190 000 kg m–3
Reference: Past Exam Paper – November 2009 Paper 11 Q19 &
Paper 12 Q18
Solution 1071:
Answer: B.
Pressure = Force / Area
Here, the force is the weight of the
metal bar. [Weight = mg]
Mass m = Density ρ × Volume V [m
= ρV]
Volume V = base area A × height h of
metal bar [V = Ah]
Weight = mg = (ρV) × g = ρAhg
Pressure P = ρAhg / A = hρg
{OR simply start with P =
hρg}
{g may be approximated to
10 ms–2 here.}
Density ρ = P / hg = 15200 / (0.80 ×
10) = 1900kg m–3
please consider answering Q20 9702/12/M/J/13
ReplyDelete9702/12/M/J/15 q36 thanks
ReplyDeleteSee solution 1118 at
Deletehttp://physics-ref.blogspot.com/2016/08/physics-9702-doubts-help-page-241.html
in solution 1069 i dont get how w is proportional to the area of the annulus?
ReplyDeletethe explanation has been updated
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