Need help answering these questions please:
1.) Suppose a car travels 108 km at a speed of 40.0
m/s, and uses 2.20 gallons of gasoline. Only 30% of the gasoline goes into useful work by the force that keeps the car moving at constant speed despite friction. (The energy content of gasoline is 1.3 ✕ 108 J per gallon.)(a) What is the force exerted to keep the car moving at constant speed?
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(b) If the required force is directly proportional to speed, how many gallons will be used to drive 108 km at a speed of 28.0 m/s?
2.) A 6.50 ✕ 105 kg subway train is brought to a stop from a speed of 0.500 m/s in 0.300 m by a large spring bumper at the end of its track. What is the force constant k of the spring?
3.) A 65.0 kg skier with an initial speed of 11.0 m/s coasts up a 2.50 m high rise as shown in Figure 6.23. Find his final speed at the top, given that the coefficient of friction between her skis and the snow is 0.0800. (Hint: Find the distance traveled up the incline assuming a straight-line path as shown in the figure.) (http://www.webassign.net/urone/6-23.gif)