A 175 lb skydiver reaches a terminal velocity of 150 mph during free fall. If the

frontal area of the diver is 8 ft2

, what are:

(a) The magnitude of the drag force acting on the skydiver?

(b) The drag coefficient?

P6.27

A 14 mm diameter sphere is dropped into a beaker of SAE 30 oil. Over a portion

of its downward motion, the sphere is measured to fall at 2 m/s. In the units of

newtons, what is the drag force acting on the test sphere?

P6.28

A low-altitude meteorological research balloon, temperature sensor, and radio

transmitter together weigh 2.5 lb. When inflated with helium, the balloon is

spherical with a diameter of 4 ft. The volume of the transmitter can be neglected

when compared to the balloon's size. The balloon is released from ground level

and quickly reaches its terminal ascent velocity. Neglecting variations in the

atmosphere's density, how long does it take the balloon to reach an altitude of

1000 ft?

P6.29

A submarine releases a spherical flotation buoy containing a radio beacon. The

buoy has a diameter of 1 ft and weighs 22 lb. The coefficient of drag for the

submerged buoy is CD = 0.45. At what steady speed will the buoy rise to

the surface?

P6.30

Place Equation (6.16) into the form of Equation (6.14) and show that the

coefficient of drag for small Reynolds numbers is given by Equation (6.15).

P6.31

(a) A luxury sports car has a frontal area of 22.4 ft2

and a 0.29 coefficient of

drag at 60 mph. What is the drag force on the vehicle at this speed?

(b) A sport-utility vehicle has CD = 0.45 at 60 mph and a slightly larger

frontal area of 29.1 ft2

. What is the drag force in this case?

P6.32

A certain parachute has a drag coefficient of CD = 1.5. If the parachute and

skydiver together weigh 225 lb, what should the frontal area of the parachute

be so that the skydiver's terminal velocity is 15 mph when approaching the

ground? Is it reasonable to neglect the buoyant force that is present?

known as a 10. A random variable that may take on any value in an interval or collection of intervals is a. continuous random variable. b. discrete random variable. c. mixed type random variable. d. multivariate random variable. e. none of the above 11. Which of the following is a required condition for a discrete probability function? a. [f(x) =0 for all values of x b. f(x) 21 for all values of x c. f(x) 0 f(x) = 0 elsewhere 170 3. Multivariate Random Variables One will recall from (1.7.27) that this pdf is known as the lognormal density and the corresponding X is called a lognormal random variable. Suppose that X, X, are iid having the common pdf f(x). Let r and s be arbitrary, but fixed real numbers. Then, obtain the expression for E [XIX;]