A car is moving at 7 m/s forward. The driver then hits the gas and 5 seconds lat

Question

A car is moving at 7 m/s forward. The driver then hits the gas and 5 seconds later the car is moving 24 m's forward. If the acceleration during this time is constant then what is the acceleration of the car while the driver has their foot on the gas? A down a road at 20 m's forward when the driver is forced to slam on A truck is driving down a road at 20 m/s forward when the driver is forced to slam on the brakes and stop the truck. If the acceleration of the truck is -5 m/s^2 forward then how long will it take the truck to stop? You throw a rock off an unknown cliff. You throw the rock straight down with an initial velocity of 15 m/s down. The rock then hits the ground 2 5 seconds later. What was the height of the cliff?

Explanation / Answer

This is a problem of kinematics, with formulas

Vf= Vo + a t

Vf2 = Vo2 + 2a X

X = Xo + Vo t + ½ g t2

Part 1

Data

V1 = 7 m/s

V2= 24 m/s

t = 5s

Vf= Vo + a t

a = (V2-V1) / t

a = (24 -7) / 5

a = 3.4 m/s2

Part 2)

Vc = 20 m/s

a =-5 m/s

Vf2= Vo2+ 2a X

Vf =0

X = -Vo2/2 a

X = - 202/ (2 (-5))

X = 40 m

Part 3)

In this case the rock is falling, so the acceleration is the acceleration of gravity

a = -g

X =Y

Y = Yo + Vo t – ½ g t2

Yo =0

Y = Vo t - ½ g t2

Y = 15 2.5 - ½ 9.8 2.52

Y = 37.5 – 30.625

Y = 6.875 m

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