Question

As a car traveling to the right passes you, you look at your watch and measure the speed of the car. The watch reads 16.0 seconds. The speed of the car is 20 m/s. The car also starts to accelerate at a constant rate when it passes you. 15 meters down the road to the right, the car is measured to be traveling at 10 m/s to the right.

1/ What kind of a problem is this?

2/ What is the direction of the acceleration of the car?

3/ What is the acceleration of the car? Answer using an integer in m/s/s.

4/What time is on the watch when the car is 15 meters down the road? Answer using an integer in seconds.

Answer 1

Solution:

Using the information given,

1.) This is a Linear kinematics related problem.

2.) Ans: Left,

Reason: As the car's velocity is reducing from 20 m/s to 10 m/s means car has a negative acceleration which is left is direction.

3.) Using kinematics eq,

v² - u² = 2aS

a = v² - u²/2S

= 10² - 20²/2*15

= - 10 m/s2 or 10 m/s2 left.

4.) Time taken by the car to reduce its velocity is

t = v - u /a

= 10 - 20/ -10

= 1 s

So, the watch reads = 16 s + 1s = 17 s.

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