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Chapter 8: Q111P (page 211)
A 9.40 kgprojectile is fired vertically upward. Air drag decreases the mechanical energy of the projectile-Earth system by 68.0 kJduring the projectile鈥檚 ascent. How much higher would the projectile have gone were air drag negligible?
The height is h=738 m .
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A 50 gball is thrown from a window with an initial velocity of 8.0 m/sat an angle ofabove the horizontal. Using energy methods, determine (a) the kinetic energy of the ball at the top of its flight and (b) its speed when it is 3.0 mbelow the window. (c)Does the answer to part (b) depend on either (c) the mass of the ball or (d) the initial angle?
The temperature of a plastic cube is monitored while the cube is pushed 3.0 macross a floor at constant speed by a horizontal force of 15 N. The thermal energy of the cube increases by 20 J. What is the increase in the thermal energy of the floor along which the cube slides?
A volcanic ash flow is moving across horizontal ground when it encounters aupslope. The front of the flow then travels 920 mup the slope before stopping. Assume that the gases entrapped in the flow lift the flow and thus make the frictional force from the ground negligible; assume also that the mechanical energy of the front of the flow is conserved. What was the initial speed of the front of the flow?
During a rockslide, a 520 kgrock slides from rest down a hillside that islong and 300 mhigh. The coefficient of kinetic friction between the rock and the hill surface is 0.25. (a) If the gravitational potential energy Uof the rock鈥揈arth system is zero at the bottom of the hill, what is the value of U just before the slide? (b) How much energy is transferred to thermal energy during the slide? (c) What is the kinetic energy of the rock as it reaches the bottom of the hill? (d) What is its speed then?
The maximum force you can exert on an object with one of your back teeth is about 750 N. Suppose that as you gradually bite on a clump of licorice, the licorice resists compression by one of your teeth by acting like a spring for which . Find (a) the distance the licorice is compressed by your tooth and (b) the work the tooth does on the licorice during the compression. (c) Plot the magnitude of your force versus the compression distance. (d) If there is a potential energy associated with this compression, plot it versus compression distance. In the 1990s the pelvis of a particular Triceratops dinosaur was found to have deep bite marks. The shape of the marks suggested that they were made by a Tyrannosaurus rex dinosaur. To test the idea, researchers made a replica of a T. rex tooth from bronze and aluminum and then used a hydraulic press to gradually drive the replica into cow bone to the depth seen in the Triceratops bone. A graph of the force required versus depth of penetration is given in Fig. 8-71 for one trial; the required force increased with depth because, as the nearly conical tooth penetrated the bone, more of the tooth came in contact with the bone. (e) How much work was done by the hydraulic press鈥攁nd thus presumably by the T. rex鈥攊n such a penetration? (f) Is there a potential energy associated with this penetration? (The large biting force and energy expenditure attributed to the T. rex by this research suggest that the animal was a predator and not a scavenger.)
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