A car travels 40 miles in 30 minutes.

a) What is the average velocity in kilometers/hour?

b) If the car weighs 1.5 tons, what is its kinetic energy in joules (Note: you will need to convert your velocity to m/s) ?

c) When the driver applies the brake, it takes 15 seconds to stop. How far does the car travel (in meters) while stopping?

d) What is the average acceleration of the car (in m/s2) during braking?

a) v = 160.9 Km / h, b) K = 9,988 10⁵ J, c) d = 335.2 m, d) a = - 2.9796 m / s²

Explanation:

a) The average speed is defined as the distance traveled in the time interval

v = d / t

Let's reduce the magnitudes to the SI system

t = 30 min (60 s / 1min) = 1800 s

d = 50 mile (1609 m / 1mile) = 80450 m

v = 80450/1800

v = 44.6944 m / s

v = 44.6944 m / s (1 km / 1000m) (3600 s / 1h)

v = 160.9 Km / h

b) W = 2 ton (1000 kg / 1 ton) = 1000 kg

K = ½ m v²

K = ½ 1000 44.694²

K = 9,988 10⁵ J

c) take t = 15 s to stop

v = v₀ - at

v = 0

a = v₀ / t

a = 44,694 / 15

a = 2.9796 m / s²

v² = v₀² - 2 a d

v = 0

d = v₀² / 2 a

d = 44.694² / (2 2.9796)

d = 335.2 m

d) the average acceleration is the change of speed in the time interval

a = (v - v₀) / (t - t₀)

a = (0 - 44.694) / 15

a = - 2.9796 m / s²