At time t = 0, a 2150-kg rocket in outer space fires an engine that exerts an increasing force on it in the +x-direction. This force obeys the equation F = At^2, where t is time,
and has a magnitude of 781.25 N when r = 1.25 s. (a) Find the SI value of the constant A, including its units. (b) What impulse does the engine exert on the rocket during the I .50-s
interval starting 2.00 s after the engine is fired? (c) By how much does the rocket?s velocity change during this interval?

Respuesta :

Answer:

a)  A = 500 N/s²

b)  I = 5812.50 N-s

c)  Δv = 2.7034 m/s

Explanation:

Given info

m = 2150 kg

F(t) = At²

F(1.25 s) = 781.25 N

a) A = ?

We use the equation

F(t) = At²  ⇒     781.25 N = A*(1.25 s)²

⇒ A = F(t) / t² = (781.25 N) / (1.25 s)²

⇒ A = 500 N/s²

b) I = ?  if   2.00 s ≤ t ≤ 3.50 s

we apply the equation

I = ∫F(t) dt = ∫At² dt = A ∫t² dt = (500/3)*t³ + C

Since the limits of integration are 2 and 3.5,  we obtain

I = (500/3)*((3.5)³-(2)³) = 5812.50 N-s

c) Δv = ?

we can apply the equation

I = m*Δv   ⇒   Δv = I / m

⇒   Δv = 5812.50 N-s / 2150 kg

⇒   Δv = 2.7034 m/s

The value of constant A can be calculated by substituting the value of F and t. The impulse can be calculate by integration of given equation of f(t).

(a) The SI value of the constant A, including its units is [tex]500 \:\rm N/s^2[/tex].

(b) The impulse exerted on rocket is [tex]5812.50 \:\rm N-s[/tex].

(c) The change in velocity is [tex]2.7034 \: \rm m/s[/tex].

Given:

The rocket mass is [tex]m=2150\:\rm kg[/tex].

The time is [tex]t=1.25\: \rm s[/tex]

The magnitude is [tex]F=781.25\:\rm N[/tex]

(a)

The force obeys the equation as follows,

[tex]F = At^2[/tex]

Substitute the value.

[tex]781.25 \:\rm N =A\times(1.25 \:\rm s)^2\\A=500 \:\rm N/s^2[/tex]

(b)

What is impulse?

The impulse is defined as the integral of the force.

Calculate the impulse exerted on rocket.

[tex]I=\int F(t)\\I=\int At^2 dt\\I=A \int t^2dt\\I=\dfrac{500}{3}\times t^3+ C[/tex]

Substitute the integration limit  from 2 and 3.5 s.

[tex]I=\dfrac{500}{3}\times ((3.5)^3-(2)^3)\\I= 5812.50 \: \rm N-s[/tex]

(c)

Calculate the change in velocity.

[tex]I = m\times \Delta v\\\Delta v =\dfrac{I}{m}[/tex]

Substitute the value.

[tex]\Delta v=\dfrac{5812.50\:\rm N-s}{2150 \: \rm kg}\\\Delta v=2.7034\:\rm m/s[/tex]

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