Answer
$F=5.2\times 10^3 N$
Work Step by Step
All units must be in SI units. Therefore, speed must be converted to meters per second using dimensional analysis to get $$\frac{40km}{1hr} \times \frac{1hr}{60min} \times \frac{1min}{60s} \times \frac{1000m}{1km}$$ $$=11m/s$$ To find force, acceleration must be known. To find acceleration, use a kinematics equation relating acceleration, initial velocity, final velocity, and distance, which is $$v_f^2=v_o^2+2a\Delta x$$ Solving for $a$ yields $$a=\frac{v_f^2-v_o^2}{2\Delta x}$$ Substituting known values of $v_o=11m/s$, $v_f=0.0m/s$, and $\Delta x=15m$ yields an acceleration of $$a=\frac{-(11m/s)^2}{2(15m)}=-4.0m/s^2$$ Force is defined as $$F=ma$$ The force of weight is $w=mg$, so $m=\frac{w}{g}=\frac{1.30\times 10^4N}{9.80m/s^2}=1.33\times 10^3kg$. Substituting this mass value and acceleration value yields a force of $$F=ma=(1.33\times 10^3kg)(4.0m/s^2)=5.2\times 10^3 N$$
