C. 400 km/min
1 answer:
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The final velocity of the car is +1.5 m/s.
Explanation:
We have to divide the problem into two parts.
In the first part, the car starts from rest and accelerates for 5.0 s. We can find the final velocity of the car after this first part using the suvat equation:
where
v is the final velocity
u = 0 is the initial velocity
is the acceleration
t = 5.0 s is the time
Substituting,
In the second part, the brakes are applied, so the car decelerates for 3.0 s, and the final velocity is given by
where
v' is the final velocity
v = 7.5 m/s is the velocity at the beginning of this part
is the deceleration
t = 3.0 s is the time
Substituting,
So, the final velocity is +1.5 m/s.
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Answer:
a) the reflective surface has twice the energy transfer
b) A = 1.3 10²⁷ km²
c) the energy emitted by the sun is distributed in a sphere that depends on the square of the distance, and the gravitational force depends on the square of the distance
Explanation:
a) The pressure exerted on the candle is related to the variation of the momentum
P =
in a case of absorption (inelastic shock) all the energy is absorbed therefore the pressure is
P = \frac{1}{c} \ \frac{dp}{dt}
in the case of reflection (elastic shock) an energy is absorbed by absorbing the light and then by action and reaction the same energy is absorbed in the reflected light
P = 2 \frac{1}{c} \ \frac{dp}{dt}
In conclusion, the reflective surface has twice the energy transfer.
b) pressure is defined with force per unit area
P = F / A
F = P A
this force must be greater than the gravitational force of attraction of the sun
Fg = G m Ms / r²
let's look for the case that the two forces are equal
F = Fg
P A_sail = G m Ms = r²
suppose a fully reflective sail
The pointing vector is the power delivered per unit area
S = I = P / A
where A is the area of the sphere where the is distributed by the sun
A = 4π r²
we substitute
A_{sail} = G m M_s
A = G m M_s 2π c
let's calculate
A = 6.67 10⁻¹¹ 10000 2 10³⁰ 2π 3 10⁸
A = 1,257 10³³ m²
let's reduce to km²
A = 1.3 10³³ m² (1km / 10³ m) ²
A = 1.3 10²⁷ km²
c) The size of the candle is independent of the distance to the sun because the energy emitted by the sun is distributed in a sphere that depends on the square of the distance, and the gravitational force depends on the square of the distance, therefore the two dependencies are canceled.