Question

extra practice to study:
regents practice problem: a 1200 kg car decelerates from 25 m/s to rest in 4.0 seconds during a crash.
a) calculate the acceleration.
b) calculate the net force on the car.
c) explain one design feature that could reduce this force (use physics vocabulary).

Explanation:

Step1: Define acceleration formula

Acceleration $a = \frac{v_f - v_i}{t}$, where $v_f=0$ m/s, $v_i=25$ m/s, $t=4.0$ s.

Step2: Calculate acceleration

$a = \frac{0 - 25}{4.0} = -6.25$ m/s².

Step3: Define net force formula

Net force $F = m \cdot a$, where $m=1200$ kg, $a=-6.25$ m/s².

Step4: Calculate net force

$F = 1200 \times (-6.25) = -7500$ N.

Step5: Explain force-reducing design

Increasing collision time (e.g., crumple zones) decreases acceleration (since $a=\frac{\Delta v}{t}$), so force ($F=ma$) reduces.

Answer:

a) $-6.25$ m/s²
b) $-7500$ N
c) Crumple zones: They increase collision time, decreasing acceleration (by $a=\frac{\Delta v}{t}$), thus reducing net force (by $F=ma$).