Question

A car moving at 70 km/hr has a mass of 1700 kg. What force is necessary to decelerate it at a rate of 40 cm/s/s?

Answer 1

`F= -680 N`

Explanation:

`"Force" = "mass"*"acceleration"`
Ref: Newton's 2nd Law commonly written `F= m*a`

The acceleration is -40 cm/s/s. (I added the negative sign to the given deceleration rate because the acceleration is in the direction opposite the velocity.) That data needs to be converted to have units of `m/s^2`.

`-40 "cm/s/s" = -40 cancel("cm")/s^2 * (1 m)/(100 cancel(cm)) = -0.4 m/s^2`

Plugging our data into `F= m*a`,

`F= 1700 kg*(-0.4 m/s^2) = -680 kg*m/s^2 = -680 N`

Minus sign indicate that force is in opposite direction.

I hope this helps.