Problem 2.63 A car in stop-and-go traffic starts at rest, moves forward 22 m in

Question

Problem 2.63

A car in stop-and-go traffic starts at rest, moves forward 22 m in 8.0 s, then comes to rest again. The velocity-versus-time plot for this car is given in the figure(Figure 1) .

Part A

What distance does the car cover in the first 4.0 seconds of its motion?

Express your answer using two significant figures.

8.8

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Correct

Part B

What distance does the car cover in the last 2.0 seconds of its motion?

Express your answer using two significant figures.

4.4

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Correct

Part C

What is the constant speed V that characterizes the middle portion of its motion?

Express your answer using two significant figures.

4.4

Problem 2.63

A car in stop-and-go traffic starts at rest, moves forward 22 m in 8.0 s, then comes to rest again. The velocity-versus-time plot for this car is given in the figure(Figure 1) .

Part A

What distance does the car cover in the first 4.0 seconds of its motion?

Express your answer using two significant figures.

d =

8.8

  m  

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Correct

Part B

What distance does the car cover in the last 2.0 seconds of its motion?

Express your answer using two significant figures.

d =

4.4

  m  

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Correct

Part C

What is the constant speed V that characterizes the middle portion of its motion?

Express your answer using two significant figures.

V =

4.4

  m/s   8 6 4 2 (s/u) ApoPA

Explanation / Answer

Let Distance travelled from 0-4 sec be s1
Let Distance travelled from 4-6 sec be s2
Let Distance travelled from 6-8 sec be s3

s1 = ut + (1/2)a*t^2
s1 = 0 + (1/2)a*4^2
s1 = 8a

v = u + at
v = 4a

s2 = 4a*2 = 8a

s3 = ut + (1/2)a*t^2
s3 = 4a*2 + (1/2)(-2a)*2^2
s3 = 8a - 4a
s3 = 4a

s1 + s2 + s3 = 8a + 8a + 4a = 22
20a = 22
a = 22/20
a = 11/10 = 1.1

Part A)
s1 = 8a
s1 = 8*1.1 = 8.8 m

s2 = 8a = 8.8 m

Part B)
s3 = 4a = 4.4 m

Part C)
v = 4a = 434 m/s

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