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A small space probe, of mass\(240\;{\rm{kg}}\)is launched from a spacecraft near Mars. It travels toward the surface of Mars, where it will land. At a time\(20.7\;{\rm{s}}\)after it is launched, the probe is at the location\(\left\langle {4.30 \times {{10}^3},8.70 \times {{10}^2},0} \right\rangle {\rm{m}}\)and at this same time its momentum is\(\)\(\left\langle {4.40 \times {{10}^4}, - 7.60 \times {{10}^3},0} \right\rangle \;{\rm{kg}} \cdot {\rm{m/s}}\)At this instant, the net force on the probe due to the gravitational pull of Mars plus the air resistance acting on the probe is\(\left\langle { - 7 \times {{10}^3}, - 9.2 \times {{10}^2},0} \right\rangle \;{\rm{N}}\)Assuming that the net force on the probe is approximately constant over this time interval, what are the momentum and position of the probe\(20.9\;{\rm{s}}\)after it is launched? Divide the interval into two-time steps, and use the approximation\({\vec v_{{\rm{avg}}}} \approx {\vec p_f}/m\)

Short Answer

Expert verified

The required final momentum is\(\left\langle {4.26 \times {{10}^4}, - 7.784 \times {{10}^3},0} \right\rangle \;{\rm{kg}} \cdot {\rm{m/s}}\)andthe final position is\(\left\langle {4.34 \times {{10}^3},8.64 \times {{10}^2},0} \right\rangle \;{\rm{m}}\)

Step by step solution

01

Given

Mass \(240\;{\rm{kg}}\)

At given time location and momentum are given by \(20.7\;{\rm{s}}\)

\(\left\langle {4.30 \times {{10}^3},8.70 \times {{10}^2},0} \right\rangle {\rm{m}}\)

\(\left\langle {4.40 \times {{10}^4}, - 7.60 \times {{10}^3},0} \right\rangle \;{\rm{kg}} \cdot {\rm{m/s}}\)

Resistance acting on the probe is \(\left\langle { - 7 \times {{10}^3}, - 9.2 \times {{10}^2},0} \right\rangle \;{\rm{N}}\)

02

The concept of momentum and impulse

The product of an object's mass and its speed is defined as the momentum expression.

\(p = mv\)

The mass of the item is\(m\), and the speed of the object is\(v\).

The product of force\(F\)and time is defined as the impulse, which is stated as follows:

\(I = {F_{net}}\Delta t\)

Where,\(\Delta t\)is the time taken.

03

Find the value of final momentum by applying change in momentum formula

The change in momentum can alternatively be defined as an impulse:\(I = {p_f} - {p_i}\)

The ultimate momentum is\({p_f}\), while the beginning momentum is.

The time interval is now as follows to determine the final momentum:\(\begin{aligned}{c}\Delta t = (20.9\;{\rm{s}}) - (20.7\;{\rm{s}})\\ = 0.2\;{\rm{s}}\end{aligned}\)

The required time period can be divided into two halves, one for each stage.\(0.1\;\;{\rm{s}}\).

Rearrange the equation\(I = {p_f} - {p_i}\)for\({p_f}\)and substitute\({F_{{\rm{net }}}}\Delta t\)for\(I\)

\(\begin{aligned}{c}I &= {p_f} - {p_i}\\{p_f} &= {p_i} + I\\ &= {p_i} + \left( {{F_{{\rm{net }}}}\Delta t} \right)\end{aligned}\)

Substitute\( < - 7 \times {10^3}, - 9.2 \times {10^2},0 > {\rm{N}}\)for\({F_{{\rm{net }}}}\),\( < 4.40 \times {10^4}, - 7.60 \times {10^3},0 > {\rm{kg}} \cdot {\rm{m/s}}\)for\({p_i}\),and\(0.1\;\;{\rm{s}}\)for\(\Delta t\).

\(\begin{aligned}{c}{p_f} &= {p_t} + \left( {{F_{{\rm{net }}}}\Delta t} \right)n\\ &= \left( { < 4.40 \times {{10}^4}, - 7.60 \times {{10}^3},0 > {\rm{kg}} \cdot {\rm{m}}/{\rm{s}}} \right) + \left( { < - 7 \times {{10}^3}, - 9.2 \times {{10}^2},0 > {\rm{N}}} \right)(0.1\;{\rm{s}})n\\ &= \left( { < 4.40 \times {{10}^4}, - 7.60 \times {{10}^3},0 > {\rm{kg}} \cdot {\rm{m}}/{\rm{s}}} \right) + \left( { < - 0.7 \times {{10}^3}, - 0.92 \times {{10}^2},0 > {\rm{N}} \cdot {\rm{s}}} \right)\\ &= < 4.33 \times {10^4}, - 7.692 \times {10^3},0 > {\rm{kg}} \cdot {\rm{m}}/{\rm{s}}\end{aligned}\)

04

Find the final position.

The approximation for given condition

\({v_{{\rm{avg }}}} = \frac{{{p_f}}}{m}\),

The expression for the position is,

\({r_f} = {r_i} + {v_{{\rm{avg }}}}\Delta t\)

Substitute\(\frac{{{p_f}}}{m}\)for\({v_{{\rm{avg}}}}\)

\({r_f} = {r_i} + \left( {\frac{{{p_f}}}{m}} \right)\Delta t\)

Substitute\(\left\langle {4.30 \times {{10}^3},8.70 \times {{10}^2},0} \right\rangle {\rm{m}}\)for\({r_i}\)\(\left\langle {4.33 \times {{10}^4}, - 7.692 \times {{10}^3},0} \right\rangle {\rm{kg}} \cdot {\rm{m}}/{\rm{s}}\)for\({p_f}\),\(240\;{\rm{kg}}\)for\(m\), and\(0.1\;{\rm{s}}\)for\(\Delta t\).

\(\begin{aligned}{c}{r_f} &= {r_i} + \left( {\frac{{{p_f}}}{m}} \right)\Delta t\\ &= \left( {\left\langle {4.30 \times {{10}^3},8.70 \times {{10}^2}} \right\rangle ,0{\rm{m}}} \right) + \left( {\frac{{\left\langle {4.33 \times {{10}^4}, - 7.692 \times {{10}^3},0} \right\rangle \;{\rm{kg}} \cdot {\rm{m}}/{\rm{s}}}}{{(240\;{\rm{kg}})}}} \right)(0.1\;{\rm{s}})\\ &= \left( {\left\langle {4.30 \times {{10}^3},8.70 \times {{10}^2}} \right\rangle ,0{\rm{m}}} \right) + \left( {\left\langle {0.018 \times {{10}^3}, - 0.032 \times {{10}^2},0} \right\rangle {\rm{m}}} \right)\\ = \left\langle {4.318 \times {{10}^3},8.668 \times {{10}^2}} \right\rangle ,0{\rm{m}}\end{aligned}\)

The final position and momentum of the previous step is now the initial position and momentum for the second step of\(0.1\;{\rm{s}}\),Then it follows:

Substitute\(\left\langle { - 7 \times {{10}^3}, - 9.2 \times {{10}^2},0} \right\rangle {\rm{N}}\)for\({F_{{\rm{net }}}}\),\(\left\langle {4.33 \times {{10}^4}, - 7.692 \times {{10}^3},0} \right\rangle {\rm{kg}} \cdot {\rm{m}}/{\rm{s}}\)for\({p_t}\),and\(0.1\;{\rm{s}}\), for\(\Delta t\).

\(\begin{aligned}{c}{p_f} &= {p_f} + \left( {{F_{net}}\Delta t} \right)n\\ &= \left( {\left\langle {4.33 \times {{10}^4}, - 7.692 \times {{10}^3},0} \right\rangle {\rm{kg}} \cdot {\rm{m/s}}} \right) + \left( {\left\langle { - 7 \times {{10}^3}, - 9.2 \times {{10}^2},0} \right\rangle {\rm{N}}} \right)(0.1\;{\rm{s}})\\ &= \left( {\left\langle {4.33 \times {{10}^4}, - 7.692 \times {{10}^3},0} \right\rangle {\rm{kg}} \cdot {\rm{m/s}}} \right) + \left( {\left\langle { - 0.7 \times {{10}^3}, - 0.92 \times {{10}^2},0} \right\rangle {\rm{N}} \cdot {\rm{s}}} \right)\\ &= \left\langle {4.26 \times {{10}^4}, - 7.784 \times {{10}^3},0} \right\rangle {\rm{kg}} \cdot {\rm{m/s}}\end{aligned}\)

Thus, the required final momentum is \(\left\langle {4.26 \times {{10}^4}, - 7.784 \times {{10}^3},0} \right\rangle \;{\rm{kg}} \cdot {\rm{m/s}}\)

05

Find the value of final position

Let Substitute\(\left\langle {4.318 \times {{10}^3},8.668 \times {{10}^2},0} \right\rangle {\rm{m}}\)for\({r_i}\),\(\left\langle {4.26 \times {{10}^4}, - 7.784 \times {{10}^3},0} \right\rangle {\rm{kg}} \cdot {\rm{m/s}}\)for\({p_f}\)\(240\;{\rm{kg}}\)for\(m\),and\(0.1\;{\rm{s}}\)for\(\Delta t\),\(\left\langle { - 1.37,0,0.96} \right\rangle {\rm{m}}\)for\({r_f}\),in\({r_f} = {r_i} + \left( {\frac{{{p_f}}}{m}} \right)\Delta t\)

\(\begin{aligned}{c}{r_f} &= {r_i} + \left( {\frac{{{p_f}}}{m}} \right)\Delta t\\ &= \left( {\left\langle {4.318 \times {{10}^3},8.668 \times {{10}^2},0} \right\rangle {\rm{m}}} \right) + \left( {\frac{{\left\langle {4.26 \times {{10}^4}, - 7.784 \times {{10}^3},0} \right\rangle {\rm{kg}} \cdot {\rm{m}}/{\rm{s}}}}{{(240\;{\rm{kg}})}}} \right)(0.1\;{\rm{s}})\\ &= \left( {\left\langle {4.318 \times {{10}^3},8.668 \times {{10}^2},0} \right\rangle {\rm{m}}} \right) + \left( {\left\langle {0.0187 \times {{10}^3}, - 0.0324 \times {{10}^2},0} \right\rangle {\rm{m}}} \right)\\ &= \left\langle {4.34 \times {{10}^3},8.64 \times {{10}^2},0} \right\rangle \;{\rm{m}}\end{aligned}\)Thus, the required final position is \(\left\langle {4.34 \times {{10}^3},8.64 \times {{10}^2},0} \right\rangle \;{\rm{m}}\)

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