Multiple-Choice Questions

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.)