Sally has a car that accelerates at 5 m/s^2 if the car has a mass of 1000kg how much force does the car produce

You have to use the equation F=ma.
F: the force an object has (in this case the unknown)
m: the mass an object has (in this case 1000kg)
a: the acceleration an object has (in this case 5m/s²)
when you plug everything in you should get F=5000N

I hope this helps.  Let me know if anything is unclear.