Question

Calculating average speed and acceleration in the following three linked questions below.

1. A car is traveling along a straight and horizontal road at a speed of 15 m/s. If its speed changes to 25 m/s in 2.6 s, the acceleration of the car is?

a. 6.3 m/s^2

b. 3.8 m/s^2

c. 2.5 m/s^2

d. 4.0 m/s^2

2. A car is traveling along a straight and horizontal road at a speed of 15 m/s. If its speed changes to 25 m/s in 4.0 s at a constant rate, the average speed during this period is

a. 160 m/s

b. 40 m/s

c. 20 m/s

d. 80 m/s

3. A car is traveling along a straight and horizontal road at a speed of 15 m/s. If its speed changes to 25 m/s in 4.0 s at a constant rate, the distance traveled by the car during the acceleration period is

a. 160 m

b. 40 m

c. 20 m

d. 80 m

Answer 1

v_i = 15 m/s v_j = 25 m/s t = 2.6 s a = v_j - v_i/t = 25 - 15/2.6 = 3.846 m/s^2 b= 3.8 m/s^2 v_i = 15 m/s, v_j = 25 m/s, t = 4s a = v_j - v_i/t = 25 - 15 = 4 = 2.5 m/s^2 S = v_i t + 1/2 a t^2 Average speed = S/t = v_i + 1/2 a t = 15 + 1/2 times 2.5 times 4 = 15 + 5 = 20 m/s v_average = 20 m/s c a = v_j - v_i/t = 25 - 15/4 = 2.5 m/s^2 v^2_j -v^2_i = 2as rightarrow S = 25^2 - 15^2/2 times 2.5 = 80 m S = 80 m d