Answer :
Answer:
a) t = 0.622 s , v = 7.73 m / s , b) K = 2539 J , c) -2443.4 J , d) fr = 803.75 N
Explanation:
A) when the fireman from the second floor is in a free fall motion the time to arrive, we can calculate it with kinematics
y = v t + ½ g t²
When you jump your initial speed is zero
y = ½ g t²
t = √2y / g
Let's reduce the magnitude to the SI system
y = 10 feet (0.3048 / 1 foot) = 3,048 m
t = √ (2 3,048 /9.8)
t = 0.622 s
The speed at this point is
v² = v₀² + 2 g y = 0 + 2g y
v = √ (2 9.8 3.048)
v = 7.73 m / s
B) The kinetic energy is
K = ½ m v²
K = ½ 85 7.73²
K = 2539 J
C) The relationship between work and kinetic energy is
W = ΔK = [tex]K_{f}[/tex] - K₀
The initial kinetic energy is zero because when its high speed is zero.
[tex]K_{f}[/tex] = ½ m v²
[tex]K_{f}[/tex]= ½ 85 1.5²
[tex]K_{f}[/tex] = 95.6 J
W2 = 95.6 - 0 = 95.6 J
The variation of work in free fall less with friction
ΔW = W2 -W
Δw = 95.6 -2539
ΔW = -2443.4 J
This is the work done by the friction forces
C)
W2 = fr d cos θ
The angle is 180º because the friction opposes the movement
W2 = - fr d = -2443.4
fr = 2443.4 / d = 2443.4 / 3,048
fr = 803.75 N