Concept explainers
(a)
The number of times terminal speed greater than for steel sphere that of the wooden sphere.
(a)

Answer to Problem 92P
The steel’s sphere terminal speed is 4 times greater than for the velocity of wooden sphere.
Explanation of Solution
Write the expression for terminal velocity of the object.
vterm=√2mgρA (I)
Here, m is the mass, g is the acceleration due to gravity, ρ is the density of air, and A is the cross section area of the object.
The cross sectional area of the sphere is,
A=πr2=π(d2)2 (II)
Here, r is the radius of the sphere and d is the diameter of the sphere.
Rewrite the above equation for terminal velocity of wooden sphere.
vterm(wood)=√2mgρAwood (III)
Here, Awood is the cross section area of the wooden sphere.
Rewrite the equation (I) for terminal velocity of steel sphere.
vterm(steel)=√2mgρAsteel (IV)
Here, Asteel is the cross section area of the steel sphere.
Conclusion:
Solve the equation (III) and (IV).
vterm(wood)vterm(steel)=√2mgρAwood√2mgρAsteel=√AsteelAwood
Rewrite the above relation by using equation (2).
vterm(wood)vterm(steel)=√π(dsteel2)2π(dwood2)2=√(dsteel)2(dwood)2=dsteeldwood
Substitute 40 cm for dwood and 10 cm for dsteel in above relation.
vterm(wood)vterm(steel)=10 cm40 cmvterm(wood)vterm(steel)=14vterm(wood)=14vterm(steel)
Therefore, the steel’s sphere terminal speed is 4 times greater than for the velocity of wooden sphere, due to its smaller cross sectional area.
(b)
The ratio of the terminal speed of the steel sphere to that of wooden sphere.
(b)

Answer to Problem 92P
The terminal velocity of the steel sphere is twice the velocity of the wooden sphere due to its higher mass.
Explanation of Solution
From part (a),
The ratio of the terminal speed of the steel sphere to that of wooden sphere for different mass of the sphere with same cross sectional area is,
vterm(wood)vterm(steel)=√2mwoodgρA√2msteelgρA=√mwoodmsteel
Conclusion:
Substitute 40 kg for msteel and 10 kg for mwood in above relation.
vterm(wood)vterm(steel)=√10 kg40 kgvterm(wood)vterm(steel)=12vterm(wood)=12vterm(steel)
Therefore, the terminal velocity of the steel sphere is twice the velocity of the wooden sphere due to its higher mass.
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Chapter 3 Solutions
Bundle: College Physics: Reasoning And Relationships, 2nd + Webassign Printed Access Card For Giordano's College Physics, Volume 1, 2nd Edition, Multi-term
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