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A motorist is driving at 20 m/s when she sees that a
Chapter 2, Problem 63P(choose chapter or problem)
Problem 63P
A motorist is driving at 20 m/s when she sees that a traffic light 200 m ahead has just turned red. She knows that this light stays red for 15 s, and she wants to reach the light just as it turns green again. It takes her 1.0 s to step on the brakes and begin slowing. What is her speed as she reaches the light at the instant it turas green?
Questions & Answers
QUESTION:
Problem 63P
A motorist is driving at 20 m/s when she sees that a traffic light 200 m ahead has just turned red. She knows that this light stays red for 15 s, and she wants to reach the light just as it turns green again. It takes her 1.0 s to step on the brakes and begin slowing. What is her speed as she reaches the light at the instant it turas green?
ANSWER:
Step 1 of 3
We have to find the speed of the motorist as she reaches the light at the instant it turns green.
The distance travelled by the motorist in the time it takes her to step on the brakes and begin slowing can be found from the equation.
\(s_{f}=s_{i}+v_{i s} \Delta t\)
Where,
\(s_{f}=s_{1} \text { in } \mathrm{m}\)
\(s_{i}=s_{0}=0 \mathrm{~m}\)
\(v_{t z}=v_{o}=20 \mathrm{~m} / \mathrm{s}\)
\(\Delta t=1.0 \mathrm{~s}\)
Thus,
\(s_{1} =0+(20)(1.0)\)
\(=20 \mathrm{~m}\)