Answer:
1000 N
Explanation:
First, we need to find the deceleration of the running back, which is given by:

where
v = 0 is his final velocity
u = 5 m/s is his initial velocity
t = 0.5 s is the time taken
Substituting, we have

And now we can calculate the force exerted on the running back, by using Newton's second law:

so, the magnitude of the force is 1000 N.
I would have to say B failed because I think I read something about it being only 2law not 3
Answer:
T = 693.147 minutes
Explanation:
The tank is being continuously stirred. So let the salt concentration of the tank at some time t be x in units of kg/L.
Therefore, the total salt in the tank at time t = 1000x kg
Brine water flows into the tank at a rate of 6 L/min which has a concentration of 0.1 kg/L
Hence, the amount of salt that is added to the tank per minute = 
Also, there is a continuous outflow from the tank at a rate of 6 L/min.
Hence, amount of salt subtracted from the tank per minute = 6x kg/min
Now, the rate of change of salt concentration in the tank = 
So, the rate of change of salt in the tank can be given by the following equation,

or, 
or, T = 693.147 min (time taken for the tank to reach a salt concentration
of 0.05 kg/L)