A 40g bullet traveling at 450 m/s passed through a board and comes out traveling 300m/s. The board is 7.6cm thick. What is the force of friction applied by the wood to the bullet?

f = 29605.2 [N]

Explanation:

To solve this problem we must use the following equation of kinematics, then use Newton's second law.

where:

Vf = final velocity = 300 [m/s]

Vo = initial velocity = 450 [m/s]

a = acceleration [m/s²]

x = distance = 7.6 [cm] = 0.076 [m]

Now replacing and clearing a

2*a*0.076 = (450² - 300²)

a = 740131.57 [m/s²]

Now using Newton's second law which tells us that the force on a body is equal to the product of mass by acceleration.

f = m*a

where:

f = friction force [N]

m = mass = 40 [g] = 0.04 [kg]

f = 0.04*740131.57

f = 29605.2 [N]

d₁ = displacement of tern from arctic to antarctic = 11000 miles

d₂ = displacement of tern from antarctic to arctic =   - 11000 miles

d = total displacement for the journey

total displacement for the journey is given as

d = d₁ + d₂

d = 11000 + (-11000)

d = 0 miles

t₁ = time of travel from arctic to antarctic = 3 months = 3 x 30 days = 90 days

t₂ = time of travel from antarctic to arctic = 3 months = 3 x 30 days = 90 days

t = total time of travel

total time of travel is given as

t = t₁ + t₂

t = 90 + 90

t = 180 days

average velocity is given as

average velocity = total displacement/ total time

v = d/t

v = 0/180

v = 0 miles/day

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.