Wolfson Eup3 Ch12 Test Bank

Essential University Physics, 3e (Wolfson) 3e (Wolfson) Chapter 12 Static Equilibrium

1 2. 1 Co nc e pt ua lQue s t i o ns 1) If the torque on an object adds up to zero A) the forces on it also add up to zero. B) the object is at rest. C) the object cannot be turning. D) the object could be accelerating linearly but it could not be turning. E) the object could be both turning and accelerating linearly. Anser! E "ar! 1

#) A hea$y boy and a lighteight girl are balanced on a %assless seesa. If they both %o$e forard so that they are one&half their original distance fro% the pi$ot point' hat ill happen to the seesa( Assu%e Assu%e that both people are s%all enough co%pared to the length of the seesa to be thought of as point %asses. A) It is i%possible to say ithout noing the %asses. B) It is i%possible to say ithout noing the distances. C) *he side the boy is sitting on ill tilt donard. D) +othing ill happen, the seesa ill still be balanced. E) *he side the girl is sitting on ill tilt donard. Anser! D "ar! 1

1 2. 2 Pr o bl e ms ms 1) A light board' 1- % long' is supported by to sahorses' one at one edge of the board and a second at the %idpoint. A s%all s%all -&+ eight is placed beteen the to sahorses' /.- % fro% the edge and #.- % fro% the center. 0hat forces are eerted by the sahorses on the board( Anser! 12 + at the end and # + at the %idpoint "ar! 1

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#) An 5#.- g&di$er stands at the edge of a light 6.--&% di$ing board' hich is supported b y to narro pillars 1.2- % apart' as shon in the figure. 7ind the %agnitude and direction of the force eerted on the di$ing board 8a) by pillar A. 8b) by pillar B.

Anser! 8a) 1.91 + donards

8b) #.61 + upards

"ar! 1

/) A #-.-&g unifor% plan is supported by the floor at one end and by a $ertical rope at the other as shon in the figure. A 6-.-&g %ass person stands on the plan a distance three&fourths of the length plan fro% the end on the floor.

8a) 0hat is the tension in the rope( 8b) 0hat is the %agnitude of the force that the floor eerts on the plan( Anser! 8a) 22 + 8b) ##- + "ar! 1

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) A /.--&g ball rests in a frictionless groo$e as shon in the figure.

8a) 0hat is the %agnitude of the force that the left side of the groo$e eerts on the ball( 8b) 0hat is the %agnitude of the force that the right side of the groo$e eerts on the ball( Anser! 8a) #2. + 8b) #1.6 + "ar! 1

6) A nonunifor%' 5-.-&g' %eterstic balances hen the support is placed at the 61.-&c% %ar. At hat location on the %eterstic should a 6.--&g tac be placed so that the stic ill balance at the 6-.- c% %ar( A) 12.- c% B) 29.- c% C) 22.- c% D) /6.- c% E) /.- c% Anser! E "ar! 1

2) A /-.-&g child sits on one end of a long unifor% bea% ha$ing a %ass of #-.- g' and a -.-& g child sits on the other end. *he bea% balances hen a fulcru% is placed belo the bea% a distance 1.1- % fro% the /-.-&g child. :o long is the bea%( A) #.1# % B) 1.;5 % C) 1.;/ % D) #.-9 % E) #.#- % Anser! B "ar! 1

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9) In the figure' the horizontal loer ar% has a %ass of #.5 g and its center of gra$ity is 1# c% fro% the elbo joint pi$ot. :o %uch force F < %ust the $ertical etensor %uscle in the upper ar% eert on the loer ar% to hold a 9.6 g shot put(

A) 1-- + B) 6-- + C) 96- + D) 1--- + E) 16-- + Anser! D "ar! 1

5) A 6.-&% long' 1#&g unifor% ladder rests against a s%ooth $ertical all ith the botto% of the ladder /.- % fro% the all. *he coefficient of static friction beteen the floor and the ladder is -.#5. 0hat distance' %easured along the ladder fro% the botto%' can a 2-&g person cli%b before the ladder starts to slip( A) .- % B) /.9 % C) 1.9 % D) 1./ % E) /./ % Anser! C "ar! 1

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;) A stepladder consists of to hal$es' hinged at the top' and connected by a tie rod that eeps the to hal$es fro% spreading apart. In this particular instance' the to hal$es are #.6- % long' the tie rod is connected to the center of each half and is 9-.- c% long. An 5--&+ person stands /=6 of the ay up the stepladder' as shon in the figure. +eglecting the eight of the ladder' and assu%ing that the ladder is resting on a s%ooth floor' hat is the tension in the tie rod( Note: *o sol$e this proble% you %ust >cut> the ladder in half and consider the equilibriu% of forces and torques acting on each half of the ladder.

A) 1- + B) #- + C) #5- + D) /2- + E) 62- + Anser! A "ar! 1

1-) *o identical ladders are /.- % long and eigh 2-- + each. *hey are connected by a hinge at the top and are held together by a horizontal rope' 1.- % abo$e the s%ooth floor for%ing a sy%%etric >A> arrange%ent. *he angle beteen the ladders is 2 -? and both ladders ha$e their center of gra$ity at their %idpoint. 0hat is the tension in the rope( A) #- + B) /-- + C) ##- + D) #2- + E) #5- + Anser! E "ar! 1


11) A 1#-&g refrigerator' #.-- % tall and 56.- c% ide' has its center of %ass at its geo%etrical center. @ou are atte%pting to slide it along the floor by pushing horizontally on the side of the refrigerator. *he coefficient of static friction beteen the floor and the refrigerator is -./--. Depending on here you push' the refrigerator %ay start to tip o$er before it starts to slide along the floor. 0hat is the highest distance abo$e the floor that you can push the refrigerator so that it ont tip before it begins to slide( A) -.91- % B) 1.-- % C) 1.#1 % D) 1.# % E) 1.2/ % Anser! D "ar! 1

1#) A child is trying to stac to unifor% ooden b locs' 1# c% in length' so they ill protrude as %uch as possible o$er the edge of a table' ithout tipping o$er' as shon in the figure. 0hat is the %ai%u% possible o$erhang distance d (

A) 6 c% B) 2 c% C) 9 c% D) 5 c% E) ; c% Anser! E "ar! 1


1/) A unifor% sign is supported against a all at point P as shon in the figure. If the sign is a square on a side and its %ass is hat is the %agnitude of the horizontal force that the all at P eperiences(

A) #- + B) -.-- + C) 9.5 + D) ;5 + Anser! A "ar! 6-

1) A unifor% /--&g bea%' 2.-- % long' is freely pi$oted at P ' as shon in the figure. *he bea% is supported in a horizontal position by a light strut' 6.-- % long' hich is freely pi$oted at Q and is loosely pinned to the bea% at R. A load of %ass is suspended fro% the end of the bea% at S . A %ai%u% co%pression of #/'--- + in the strut is per%itted' due to safety. *he %ai%u% %ass M of the load is closest to

A) 95; g. B) 66 g. C) 1-#- g. D) 1-;- g. E) 1/#- g. Anser! A "ar! 1


16) A unifor% /--&g bea%' 2.-- % long' is freely pi$oted at P ' as shon in the figure. *he bea% is supported in a horizontal position by a light strut' 6.-- % long' hich is freely pi$oted at Q and is loosely pinned to the bea% at R. A load of %ass is suspended fro% the end of the bea% at S . A %ai%u% co%pression of #/'--- + in the strut is per%itted' due to safety. nder %ai%u% load' find the %agnitude of the x co%ponent of the force eerted on the bea% by the pi$ot at P .

A) 1/'5-- + B) 1#'5-- + C) 11'#-- + D) 1'-- + E) 12'--- + Anser! A "ar! 1


12) A 1-.-&g unifor% ladder that is #.6- % long is placed against a s%ooth $ertical all and reaches to a height of #.1- %' as shon in the figure. *he base of the ladder rests on a rough horizontal floor hose coefficient of static friction ith the ladder is -.5--. An 5-.-&g bucet of concrete is suspended fro% the top rung of the ladder' right net to the all' as shon in the figure. 0hat is the %agnitude of the friction force that the floor e erts on the ladder(

A) 6/5 + B) 9-2 + C) 1#;- + D) 5// + E) 2-1 + Anser! A "ar! 1

19) A du%p truc has a large cubical concrete bloc in its bed. *he coefficients of friction beteen this bloc and the floor of the bed are µ  -.6- and µs  -.26-. As the bed is sloly tilted abo$e the horizontal' ill the bric first begin to slide or ill it first tip o$er( A) It ill first tip o$er. B) It ill first begin to slide. C) It ill tip o$er just as it begins to slide. D) It is i%possible to anser ithout noing the %ass of the bloc. E) It is i%possible to anser ithout noing the di%ensions of the bloc. Anser! B "ar! 1

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15) A solid unifor% bric is placed on a sheet of ood. 0hen one end of the sheet is raised 8see figure)' you obser$e that the %ai%u% that the angle θ can be ithout tipping o$er the bric is ;.2?. *here is enough friction to pre$ent the bric fro% sliding. 0hat is the idth w of the bric(

A) 6.15 c% B) 2.-; c% C) 2.51 c% D) ;.- c% E) 1-.6 c% Anser! D "ar! 1

1;) A #-.-&g unifor% door has a idth of 1.#- % and a height of #.6- %. *he door is %ounted on a post by a pair of hinges' %ared 1 and # in the figure' at the top and botto% of the door. An eternal force of 2-.- +' at an angle of /-.-? abo$e the horizontal' is applied to the s%all doornob' as shon in the figure. *he doornob is 1.-- % abo$e the botto% of the door. 8a) 7ind the x co%ponent of the force that hinge 1 eerts on the door at the top. 8b) 7ind the < of the y co%ponents of the forces that hinges 1 and # together eert on the door.

Anser! 8a) &6/. +

8b) 122 +

"ar! 1

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#-) In the figure' a unifor% rectangular crate -.- % ide and 1.- % tall rests on a horizontal surface. *he crate eighs ;/- +' and its center of gra$ity is at its geo%etric center. A horizontal force F is applied at a distance h abo$e the floor. If hat %ini%u% $alue of F is required to %ae the crate start to tip o$er( tatic friction is large enough that the crate does not start to slide.

Anser! /-6 + "ar! 6-

#1) In the figure' a 1-.-&% long bar is attached by a frictionless hinge to a all and held horizontal by a rope that %aes an angle θ of 6/? ith the bar. *he bar is unifor% and eighs /;.; +. :o far fro% the hinge should a 1-.-&g %ass be suspended for the tension T in the rope to be 1#6 +(

Anser! 5.16 % fro% the hinge "ar! 1


##) In the figure' a unifor% ladder 1# %eters long rests against a $ertical frictionless all. *he ladder eighs -- + and %aes an angle θ of 9;? ith the floor. A %an eighing 9;- + cli%bs sloly up the ladder 0hen he has cli%bed to a point that is 9.5 % fro% the base of the ladder' the ladder starts to slip. 0hat is the coefficient of static friction beteen the floor and the ladder(

Anser! -.1# "ar! 6-

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Wolfson Eup3 Ch12 Test Bank

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