A 1700kg rhino charges at a speed of 50.0km/h. what average force is needed to bring the rhino to a stop in 0.50s?

From 50km/h to 0km/h in 0.5s we need next acceleration:

First we convert km/h in m/s:

50km/h = 50*1000/3600=13.8888 m/s

a = v/t = 13.88888/0.5 = 27.77777 m/s^2

Now we use Newton's law:

F=m*a

F=1700*27.7777 = 47222N