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Chapter 7: Q.55 (page 180)
What is the acceleration of the block in across the frictionless table?
Hint: Think carefully about the acceleration constraint.
The acceleration of the block is
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Blocks with masses of are lined up in a row on a frictionless table. All three are pushed forward by a force applied to the block.
a. How much force does the block exert on the block?
b. How much force does the block exert on theblock?
Your forehead can withstand a force of about before fracturing, while your cheekbone can withstand only about . Suppose a baseball traveling at strikes your head and stops in
a. What is the magnitude of the force that stops the baseball?
b. What force does the baseball exert on your head? Explain.
c. Are you in danger of a fracture if the ball hits you in the forehead? On the cheek?
The block in FIGURE EXis tied to the wall with a rope. It sits on top of the block. The lower block is pulled to the right with a tension force of . The coefficient of kinetic friction at both the lower and upper surfaces of the block is
a. What is the tension in the rope attached to the wall?
b. What is the acceleration of the block?
The cable car shown in FIGURE Pdescends a -m-high hill. In addition to its brakes, the cable car controls its speed by pulling an counterweight up the other side of the hill. The rolling friction of both the cable car and the counterweight are negligible.
a. How much braking force does the cable car need to descend at constant speed?
b. One day the brakes fail just as the cable car leaves the top on its downward journey. What is the runaway car鈥檚 speed at the bottom of the hill?
The century-old ascensores in Valparaiso, Chile, are picturesque cable cars built on stilts to keep the passenger compartments level as they go up and down the steep hillsides. As FIGURE Pshows, one car ascends as the other descends. The cars use a two-cable arrangement to compensate for friction; one cable passing around a large pulley connects the cars, the second is pulled by a small motor. Suppose the mass of both cars (with passengers) is , the coefficient of rolling friction is , and the cars move at constant speed. What is the tension in (a) the connecting cable and (b) the cable to the motor?
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