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Just 5.2 After a reaction time t0 you slam on your brakes and your wheels lock.

ID: 2997703 • Letter: J

Question

Just 5.2

After a reaction time t0 you slam on your brakes and your wheels lock. There is a constant friction force F between your wheels and the road. Ignoring air drag, find how far the car will travel after you see the deer before coming to a stop. Assume that t0 = 0.75 s, v0 = 45 mph, and mu k = 0.7. State any additional assumptions you make while solving the problem. Consider a child on a sled going down a hill of height 5 m, as depicted in Figure 5.15. You can assume the hill is frictionless. The child and sled have a mass m of 20 kg. Once on the ground, the friction brings the sled to a stop within 10 m. What is the coefficient of friction? Figure 5.15 In the log flume you are dropped from height h, and at the very bottom you are turned horizontal and brought to a stop by the water. Assume that you and the log have mass m. Is the system conservative? What is the work done by

Explanation / Answer

when boy comes from top to bottom his potential energy is changed into kinetic energy

and after that work done by frictional force decreases the kinetic energy to zero and he stops

so initial potential energy = work done by friction

mgh = ?mg*10

? = h/10 = 0.5

co efficient of friction = 0.5