If a rocket with a mass of 3500 tons vertically accelerates at a rate of 1/5 m/s^2, how much power will the rocket have to exert to maintain its acceleration at 15 seconds?
1 Answer
Explanation:
I'll assume the given mass is in metric tons.
We're asked to find the necessary power output the rocket must have so that it continues an acceleration for a certain amount of time.
Let's first find the mass of the rocket in kilograms:
m = 3500cancel("t")((10^3color(white)(l)"kg")/(1cancel("t"))) = ul(3.5xx10^6color(white)(l)"kg"
Its weight in newtons is thus
w = mg = (3.5xx10^6color(white)(l)"kg")(9.81color(white)(l)"m/s"^2) = ul(34335000color(white)(l)"N"
We're given that the acceleration of the rocket is
a = 0.2 "m/s"^2
And so by Newton's second law, the net force acting on the rocket is
sumF = ma = (3.5xx10^6color(white)(l)"kg")(0.2color(white)(l)"m/s"^2) = ul(7xx10^5color(white)(l)"N"
The only two forces acting on the rocket are
-
its weight (acting downward)
-
the thrust force originating from the rocket (acting upward)
We can find the thrust force by the equation for the net force:
sumF = F_"thrust" - w
color(red)(F_"thrust") = sumF + w = 7xx10^5color(white)(l)"N" + 34335000color(white)(l)"N" = color(red)(ul(35035000color(white)(l)"N"
Now that we know the thrust force, we can begin to calculate the work done by it:
ul(W_"thrust" = F_"thrust" · s
To find the displacement
ul(s = v_0t + 1/2at^2
The rocket started from rest, the initial velocity
ul(s = 1/2at^2
We're given
-
a = 0.2color(white)(l)"m/s"^2 -
t = 15color(white)(l)"s"
So
color(green)(s) = 1/2(0.2color(white)(l)"m/s"^2)(15color(white)(l)"s")^2 = color(green)(ul(22.5color(white)(l)"m"
The work done by the thrust force is thus
W_"thrust" = color(red)(35035000color(white)(l)"N") * color(green)(22.5color(white)(l)"m") = color(purple)(ul(7.883xx10^8color(white)(l)"J"
The power output done by the thrust is given by
ul(P_"thrust" = (W_"thrust")/t
So
color(blue)(P_"thrust") = (color(purple)(7.883xx10^8color(white)(l)"J"))/(15color(white)(l)"s") = color(blue)(ulbar(|stackrel(" ")(" "5.26xx10^7color(white)(l)"W"" ")|)
To maintain this acceleration for