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A skydiver jumps from a plane and plummets towards the earth. His or her speed does not increase...?
1.) A skydiver jumps from a plane and plummets towards the earth. His or her speed does not increase indefinitely but reaches a terminal speed of 120 miles per hour. Explain why. (static and sliding friction)
2.) When riding a horse, a jockey stands in the stirrups, legs flexing with each stride of the horse. Dirt bike riders do the same as they travel over bumpy terrain. Explain in terms of impulse and momentum.
3.) When jumping off a wall or rock you stand land with legs bent rather than straight. Why?
4.) A swimmer who jumps from a high diving board can enter the water and sustain no injury. The same person jumping from the same height and landing on concrete may not live to tell about it. Explain in terms of impulse and momentum.
1 Antwort
- Anonymvor 1 JahrzehntBeste Antwort
1) As the speed of the diver increases, so does the air resistance, which is a form of friction. However, past a certain point, the air particles are not able to move out of the way fast enough and so the friction increases suddenly, canceling out the force pushing downward (his weight). Thus, he reaches a constant velocity.
2) The jockey stands with his legs flexed because he wishes to increase the time during which the horse impacts his underside. Increasing the time elapsed is to his advantage because too much force would obviously be extremely painful, and from the definition of force: (change in momentum)/(change in time). If the time decreases, the force increases, which is bad. So by extending the time, he decreases the force. Extending the legs makes more distance to cover when the momentum changes.
3) You would land with legs bent so that the legs would bend further. If you land with straight feet, the legs don't bend properly and the time is suddenly much smaller during which all the momentum is transferred. This is extremely painful.
4) The water bends under the impact of the diver, and so increases the time during which the water's momentum is transferred to the diver. The concrete does not bend at all, and so the time is very short during which the momentum is transferred. He will die because the force is extremely large and his body cannot handle it.