350 Static Equilibrium and ElasticityQ12.9The center of gravity must be directly over the point where the chair leg contacts the floor. Thatway, no torque is applied to the chair by gravity. The equilibrium is unstable.Q12.10She can be correct. If the dog stands on a relatively thick scale, the dog’s legs on the ground mightsupport more of its weight than its legs on the scale. She can check for and if necessary correct forthis error by having the dog stand like a bridge with two legs on the scale and two on a book ofequal thickness—a physics textbook is a good choice.Q12.11If their base areas are equal, the tall crate will topple first. Its center of gravity is higher off the inclinethan that of the shorter crate. The taller crate can be rotated only through a smaller angle before itscenter of gravity is no longer over its base.Q12.12The free body diagram demonstrates that it is necessary to havefriction on the ground to counterbalance the normal force of thewall and to keep the base of the ladder from sliding. Interestingly
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