How large must the coefficient of static friction be between the tires and the road if the car is to round a level curve of radius 85m at a speed of 95 km/h?
What will be an ideal response?
Answer: We must change the given speed into units of m/s. (95,000 m/hr) (1 hr/ 3600 sec) = 26.39 m/s
The only horizontal force acting on the car is the friction force.
Ff = ?s FN and since the road is level, FN = weight of the car = m g.
Thus, Ff = ?s m g .
For circular motion this friction force is the net or centripetal force on the car .
?s m g = m v2 / R . The m's cancel out.
thus, ?s = v2 /(R g) = (26.39)2 / [(85)(9.8) ] = 0.84
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Time Dilation: A spaceship traveling at constant velocity passes by Earth and later passes by Mars. In which frame of reference is the amount of time separating these two events the proper time?
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If you are measuring the thickness of a strand of human hair, the most appropriate SI unit is the
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One end of a 0.3-m-long steel rod is connected to a wall at 204°C. The other end is connected to a wall that is maintained at 93°C. Air is blown across the rod so that a heat transfer coefficient of 17 W/(m2 K) is maintained over the entire surface. If the diameter of the rod is 5 cm and the temperature of the air is 38°C, what is the net rate of heat loss to the air?
GIVEN
FIND
The net rate of heat loss to the air (qf)
ASSUMPTIONS
The wall temperatures are constant
The system is in steady state
The rod is 1% carbon steel
The thermal conductivity of the rod is uniform and not dependent on temperature
One dimensional conduction along the rod
SKETCH
