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Sagot :
Answer:
a) P = 70054.3 W, b) P = 18820 W, c) P = 14116.7 W
Explanation:
Power is defined as work per unit of time
P = W / t = F x / t
P = F v
a) in this case the velocity is constant, let's use the equilibrium relation to find the force.
Let's set a reference system with the x axis parallel to the plane
F - Wₓ = 0
F = Wₓ
with trigonometry let's decompose the weight
sin θ = Wₓ / W
Wₓ = W sin θ
F = W sin 15
F = 2800 sin 15
F = 724.7 lb
we look for the speed, as it rises with constant speed we can use the relations of uniform motion
v = x / t
v = 1160/12
v = 96.67 ft / s
we calculate the power
P = 724.7 96.67
P = 70054.3 W
b) In this case, the speed of the vehicle changes during the ascent, so we use the relationship between work and the change in kinetic energy
W = ΔK
W = ½ m v_f² - ½ m v₀²
let's reduce to the SI system
v₀ = 10 mph (5280 ft / 1 mile) (1h / 3600 s = 14.67 ft / s
v_f = 50 mph (5280 ft / 1 mile) (1 h / 3600s) = 73.33 ft.s
mass : m = w / g
W = ½ 2800/32 (73.33² - 14.67²)
W = 225841 J
we calculate the average power
P = W / t
P = 225841/12
P = 18820 W
c) we repeat the previous procedure
v₀ = 45 mph = 66 ft / s
v_f = 15 mph = 22 ft / s
W = ½ 2800/32 (22² - 66²)
W = -169400 J
P = W / t
P = 169400/12
P = 14116.7 W
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