Answer:
a) 2457J
b) 558W
c) 337N
Explanation:
Assuming dogs started from rest.
[tex]v=a*t\\t=\frac{a}{v}\\v=12\frac{km}{h}\frac{1000m}{km}*\frac{1h}{3600s}\\\\v=3.3m/s\\\\t=\frac{3.3m/s}{0.75m/s^2}\\t=4.4s[/tex]
and the displacement is given by:
[tex]d=\frac{1}{2}*a*t^2\\d=7.3m[/tex]
Using the energy conservation formula:
[tex]K_i+U_i+W_d+W_f=K_f+U_f[/tex]
Because the motion started from rest the initial kinetic energy is zero, the motion occurred in-ground level so the gravitational energy is zero too.
the work done by the friction force is given by:
[tex]W_f=F_f*d*cos(\theta)\\W_f=\µ*m*g*d*cos(180)\\W_f=0.08*220kg*9.8m/s^2*7.3m*(-1)\\W_f=-1259J[/tex]
so:
[tex]W_d=\frac{1}{2}*220kg*(3.3m/s)^2+1259J\\W_d=2457J[/tex]
The power is given by:
[tex]P=\frac{W}{t}\\\\P=\frac{2457J}{4.4s}\\\\P=558W[/tex]
and the force exerted by the dogs:
[tex]W_d=F_d*d*cos(\theta)\\F_d=\frac{W_d}{d*cos(0)}\\\\F=\frac{2457J}{7.3m*(1)}\\\\F=337N[/tex]
