Physical Science
posted by Jessica .
A bicycle and its rider together have a mass of 80 kg. If the bicycle's speed is 6m/s, how much force is needed to bring it to a stop in 4 seconds

a= F/masstotal
vf=Vi+at
0=6+F/80 * 4
solve for F. 
a=change in vel./time
6m/s0m/s divided by 4 sec.
acc. = 1.5 m/s^2
F=ma
F= (80 kg)(1.5m/s^2)
F=120N
Hope this helps! :D 
a force of 20n gives a brick an acceleration of 5m/s^2. what force would be needed to give the brick an acceleration of 1m/s^2