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A small rocket with mass 20.0 kg is moving in free fall toward the earth. Air resistance can be neglected. When the rocket is 80.0 m above the surface of the earth, it is moving downward with a speed of 30.0 m/s. At that instant the rocket engines start to fire and produce a constant upward force F on the rocket. Assume the change in the rocket's mass is negligible. What is the value of F if the rocket's speed becomes zero just as it reaches the surface of the earth, for a soft landing? (Hint: The net force on the rocket is the combination of the upward force F from the engines and the downward weight of the rocket.)

Respuesta :

Answer:

= 308.5 N

Explanation:

acceleration  of rocket for safe landing

[tex]v_{y} ^{2} = v_{0} ^{2} +2ay[/tex]

[tex]a = \frac{v_{y}^{2} - v_{0}^{2} }{2y}[/tex]

[tex]v_{0}[/tex] = initial velocity

[tex]v_{y}[/tex] =final Velocity

m = mass of rocket

[tex]\frac{0^{2} - 30^{2} }{2\times80}[/tex]

-5.625 [tex]m/s^{2}[/tex]

Upward force

F - mg = ma

F = ma+ mg

F = m(a+g)

m= mass

a = 5.625 [tex]m/s^{2}[/tex]

g = 9.8[tex]m/s^{2}[/tex]

= 20(5.625 [tex]m/s^{2}[/tex]+ 9.8[tex]m/s^{2}[/tex])

= 308.5 N

The upward force applied on the rocket is 308.5 N.

The given parameters;

mass of the rock, m = 20 kg

speed of the rock, 30 m/s

distance traveled, h = 80 m

The acceleration of the rocket is calculated by applying third kinematic equation;

[tex]v^2 = u^2 +2ah\\\\v^2 = 2ah\\\\a = \frac{v^2 }{2h} \\\\a = \frac{(30)^2}{2(80)} \\\\a= 5.625 \ m/s^2[/tex]

The upward force applied on the rocket is calculated as follows;

F = ma + mg

F = m(a + g)

F = 20(5.625 + 9.8)

F = 308.5 N.

Thus, the upward force applied on the rocket is 308.5 N.

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