Answer:
Impulse:
![720 N\cdot s](https://img.qammunity.org/2021/formulas/physics/high-school/l45b8vis0l5n4hutvhjk0u11l89611jf77.png)
Step-by-step explanation:
The impulse experienced by an object is given by:
![I=F\Delta t](https://img.qammunity.org/2021/formulas/physics/high-school/qv4d9doyi5c8x2mljdpr19e2avo2p24l22.png)
Where
F is the magnitude of the force exerted on the object
is the time interval during which the force is applied
I is the impulse
For the halfback in this problem, we have:
F = 800 N is the force experienced
is the time interval
Therefore, the impulse experienced is
![I=(800)(0.9)=720 N\cdot s](https://img.qammunity.org/2021/formulas/physics/high-school/kbcyajk3cl8pnik7n1jru0zzkvf41bc4wc.png)
And this impulse is also equal to the change in momentum of the halfback.