Question

A student wearing frictionless roller skates moving at 1.2 m/s on a horizontal surface is then pushed by a friend 6.54 m with a constant force of 45 N. If her final kinetic energy is 352 J, what is the mass of the student? 

Answer 1

$KE=mv^2/2\to m=2\cdot KE/v^2$

$s=\frac{v^2-v_0^2}{2a}\to v^2=2as+v_0^2=2\cdot \frac{F}{m}\cdot s+v_0^2$

$m=\frac{2\cdot KE}{2\cdot \frac{F}{m}\cdot s+v_0^2}\to m=\frac{2KE-2Fs}{v_0^2}=$

$=\frac{2\cdot 352-2\cdot 45\cdot 6.54}{1.2^2}=80.14\ (kg)$ . Answer