Question

The driver of a car traveling at a speed of 20.0 m/s slams on the brakes and comes to a stop in 5.8 s. If we assume that the car's speed changed at a constant rate (constant net force), what was theaverage speed during this 5s interval?
average speed = m/s

Answer 1

Answer:

10 m/s

Explanation:

u = 20 m/s

v = 0 m/s

t = 5.8 s

Let a be the acceleration and s be the distance traveled by the car in time t.

use first equation of motion

v = u + a t

0 = 20 + a x 5.8

a = -3.45 m/s^2

Use third equation of motion

$v^{2}=u^{2}+2as$

$0^{2}=20^{2}-2 \times3.45 \times s$

s = 58 m

The average speed is defined as the ratio of distance traveled to the time taken.

$Average speed = \frac{58}{5.8} = 10 m/s$

thus, the average speed of the car is 10 m/s.