Question

A car moves with a speed of 72 km/h for 15 minutes and then with a speed of 80 km/h for the next 12 minutes. The total distance covered by the car is:

Answer 1

Answer:

The total distance covered by the car is 3,810.08 m

Explanation:

Given;

initial speed of the car, u = 72 km/hr = 20 m/s

initial time, t₁ = 15 minutes = 900 s

final speed of the car, v = 80 km/hr = 22.22 m/s

final time, t₂ = 12 minutes = 720 s

The acceleration of the car is given as;

$a = \frac{v-u}{t_2 -t_1} \\\\a = \frac{22.22-20}{900-720}\\\\a = 0.0123 \ m/s^2$

The total distance covered by the car is given as;

v² = u² + 2as

where;

s is the total distance covered by the car

22.22² = 20² + 2(0.0123)s

22.22²  - 20² = 2(0.0123)s

93.728 = 0.0246s

s = 93.728 / 0.0246

s = 3,810.08 m

Therefore, the total distance covered by the car is 3,810.08 m

Answer 2

Answer:

34 km

Explanation:

Remark

You are dealing with distance not direction. So you just figure out the two parts separately and add.

15 minutes

t = 15 minutes * 1 hour / 60 minutes = 0.25 hours.

r = 72 km / hr

d = 72 km / hr * 0.25 hours

d = 18 km

12 minutes

t = 12 minutes * 1 hour/ 60 minutes = 0.2 hours

r = 80 km/hour

d = 80 * 0.2 = 16 km

Total distance

d = d1 + d2

d = 18 + 16 = 34 km