Question

8.How long (in seconds) does it take for a caraccelerating at 3.50 m/s2 to go from rest to 120 km/h?

Answer 1

The time it takes for an object to change its velocity at a constant acceleration is given by:

$\Delta t=\frac{\Delta v}{a}$

Since the car changes its speed from 0 to 120km/h, then Δv=120km/h.

Write the change in speed using meters per second. Remember that 1m/s=3.6km/h:

$120\frac{km}{h}=120\frac{km}{h}\times\frac{1\frac{m}{s}}{3.6\frac{km}{h}}=33.333\ldots\frac{m}{s}$

Replace Δv=33.333m/s and a=3.50m/s^2 to find the time it takes for the car to reach a speed of 120km/h:

$\Delta t=\frac{33.333\ldots\frac{m}{s}}{3.50\frac{m}{s^2}}=9.52s$

Therefore, it takes 9.52 seconds for a car accelerating at 3.50m/s to go from rest to 120km/h.