# A car with a total mass of 1400kg (including occupants), traveling at 60kmh^-1 hits a large tree and stops in 0.08seconds. What is the magnitude of the deceleration of the 70kg driver of the car if he is wearing a properly fitted seat belt?

May 6, 2017

$208. \overline{3} m {s}^{-} 2$

#### Explanation:

Using the kinematic equation

$v = u + a t$
where symbols have their respective meanings. Inserting given values in SI units, and assuming that deceleration is constant, we have

$0 = \frac{60 \times {10}^{3}}{3600} + a \times 0.08$
$0 \implies a = - \frac{60 \times {10}^{3}}{3600} \times \frac{1}{0.08} = - 208. \overline{3} m {s}^{-} 2$
$- v e$ sign shows it is deceleration.

This is deceleration of car, its occupants including driver.