Animals Falling Cats
Multiple-Choice Questions
Question 1
Falling Cats
Which is the correct free body diagram for a cat immediately after falling off of a cliff? a)
b)
c)
Question 1 Solution
Falling Cats
Which is the correct free body diagram for a cat immediately after falling off of a cliff? a)
b)
c)
Force of Gravity is constant. D= ¼ A v2, so D increases as v increases
Question 2
Falling Cats
Which is the correct free body diagram for a cat that has reached terminal velocity ?
a)
b)
c)
Question 2 Solution
Falling Cats
Which is the correct free body diagram for a cat that has reached terminal velocity ?
a)
b)
For v = vterm, D = Fg
c)
Question 3
Falling Cats
An object with smaller cross sectional area A has a larger terminal velocity than an object with larger A. a) always true b) sometimes true c) never true
Question 3 Solution
Falling Cats
An object with smaller cross sectional area A has a larger terminal velocity than an object with larger A. a) always true b) sometimes true c) never true 4mg v term = ρA
€
Need to compare the ratio (m/ A), not just A alone. (Note: It will also depend on how aerodynamic the objects are in case there is a big difference in their drag coefficients.)
Question 4
Falling Cats
Which of the following describes what happens to a meteor crashing through the atmosphere travelling faster than its terminal velocity? a) The meteor decelerates b) The meteor stays at constant v c) The meteor accelerates
Question 4 Solution
Falling Cats
Which of the following describes what happens to a meteor crashing through the atmosphere travelling faster than its terminal velocity? a) The meteor decelerates b) The meteor stays at constant v c) The meteor accelerates When v > vterm , the drag force is larger than the gravitational force meaning the net force is opposite to the motion causing deceleration until v = vterm. (Note: The work done by the drag force is converted into heat, which usually causes meteorites to burn up in the atmosphere.)
Question 5 vbike
Falling Cats
vair
The magnitude of the drag on a cyclist encountering a head wind is given by a) D = ¼ ρ A (vbike)2 b) D = ¼ ρ A (vbike-vair)2 c) D = ¼ ρ A (vbike+ vair)2
Question 5 Solution vbike
Falling Cats
vair
The magnitude of the drag on a cyclist encountering a head wind is given by
D = ¼ ρ Av2 where v is the speed b) D = ¼ ρ A (vbike-vair)2 of the object relative to the air 2 c) D = ¼ ρ A (vbike+ vair) a) D = ¼ ρ A (vbike)2
Question 6 vbike
Falling Cats
vair
The magnitude of the drag on a cyclist encountering a tail wind is given by a) D = ¼ ρ A (vbike)2 b) D = ¼ ρ A (vbike-vair)2 c) D = ¼ ρ A (vbike+ vair)2
Question 6 Solution vbike
Falling Cats
vair
The magnitude of the drag on a cyclist encountering a tail wind is given by D = ¼ ρ Av2 a) D = ¼ ρ A (vbike)2 where v is the speed of the object relative 2 b) D = ¼ ρ A (vbike-vair) to the air. (Note: If vair > vobj, c) D = ¼ ρ A (vbike+ vair
)2
the drag force changes direction and the cyclist will be pushed by the wind.)