Question

A car can stop from60mph in 2.5 sec. If the car has a weight of 3225 lbs what force acts on the car?

Answer 1

Acceleration is change in velocity over time, or:
a = (v2 - v1)/t
Initial velocity (v1) and time (t) is given, and final velocity (v2) is zero since it eventually comes to rest.
Convert first the initial velocity units to ft/s, then solve for acceleration. Finally, substitute it to formula for force.

Force is mass x acceleration, or:
F = m*a
The mass (m) is given so you can solve for force.

Units of force in lb,m ft/s^2

Answer 2

60mph converts into 26.82m/s,
a= (0-26.82 m/s)
-26.82 m/s

but don't understand how to get answer in Newtons which are kg m/s^2

Answer 3

a = (Vf-Vi)/t = -26.82m/s / 2.5s = -10/73 m/s^2

Now recall F=ma

Answer 4

oops. That's -10.73, not 10/73