Question

A car decelerates uniformly at 3 m/s2 while coming to a complete halt in 7 meters. The speed of the car at the start of the deceleration is ____ m/s.

Answer 1

Answer on Question#38840, Physics, Mechanics

A car decelerates uniformly at $3\mathrm{m/s}^2$ while coming to a complete halt in 7 meters. The speed of the car at the start of the deceleration is _____ m/s.

Solution:

This equation relates final velocity, original velocity, constant acceleration, and displacement:

$$2ad = v_f^2 - v_0^2$$ $$a = 3\mathrm{m/s}^2;$$ $$d = 7\mathrm{m};$$ $$v_f = 0\mathrm{m/s}.$$

The speed of the car at the start of the deceleration is

$$v_0 = \sqrt{2ad}$$ $$v_0 = \sqrt{2 \cdot 3 \cdot 7} = \sqrt{42} = 6.48 \approx 6.5\mathrm{m/s}.$$

Answer. $6.5\mathrm{m/s}$.