The intensity I of light varies inversely as the square of the distance D from the source. If the intensity of
illumination on a screen 5 ft from a light is 4 foot candles, find the intensity on a screen 20 ft from the light.
Express the answer as a fraction.
The weight of a body above the surface of the earth varies inversely as the square of its distance from the center
of the earth. What is the effect on the weight when the distance is multiplied by 2?
The weight is multiplied by 2.
The weight is divided by 4.
The weight is divided by 2.
The weight is multiplied by 4.
The period of vibration P for a pendulum varies directly as the square root of the length L. If the period of
vibration is 4 sec when the length is 64 inches, what is the period when L =5.0625 inches?
The gravitational attraction A between two masses varies inversely as the square of the distance between them.
The force of attraction is 9 lb when the masses are 2 ft apart, what is the attraction when the masses are 6 ft
apart?
At a fixed temperature, the resistance R of a wire varies directly as the length l and inversely as the square of its
diameter d. If the resistance is 0.4 ohm when the diameter is 1 mm and the length is 200 cm, what is the
resistance when the diameter is 2 mm and the length is 1620 cm?
Wind resistance or atmospheric drag tends to slow down moving objects. Atmospheric drag varies jointly as an
object’s surface area A and velocity v. If a car traveling at a speed of 40 mph with a surface area of 37 ft2
experiences a drag of 236.8 N (Newtons), how fast must a car with 48 ft2 of surface area travel in order to
experience a drag force of 529.92 N?
The cost of stainless steel tubing varies jointly as the length and the diameter of the tubing. If a 5 foot length
with diameter 2 inches costs $48.00 , how much will a 7 foot length with diameter 5 inches cost?
The force needed to keep a car from skidding on a curve varies jointly as the weight of the car and the square of
the car’s speed, and inversely as the radius of the curve. If a force of 3600 pounds is needed to keep an
1800 pound car traveling at 20 mph from skidding on a curve of radius 600 feet, what force would be required
to keep the same car from skidding on a curve of radius 550 feet at 60 mph? Round your answer to the nearest
pound of force?