A car weighing 2.5 metric tons and traveling at 90 km/h hits a 500 m long stretch of black ice. Unfortunately, due to skidding, neither accelerating nor braking has any effect on the speed! The driver manages to maintain steady straight direction of motion and the only impact is provided by the ice friction force, which is numerically equal to 4v² Newtons, where the velocity v of the car is measured in m/sec. (a) Using Newton's Second Law F = ma, set up a mathematical model for the position x(t) and velocity v(t) of the car as functions of time t. Start by drawing a diagram and choosing a consistent system of units based on kg, m, sec (1 ton = 1000 kg, 1 m/sec = 3.6 km/h, 1 N = 1 kg · m/sec²). Introduce and label the variables, show the units and write down the differential equations and the intial conditions. (b) Use the model in part a to calculate v(t) and r(t). Fully show the process of solving the initial value problems. (c) Based on your work so far how long will it take to pass the iced over stretch of the road

Glencoe Physics: Principles and Problems, Student Edition
1st Edition
ISBN:9780078807213
Author:Paul W. Zitzewitz
Publisher:Paul W. Zitzewitz
Chapter6: Motion In Two Dimensions
Section6.3: Relative Velocity
Problem 27PP
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A car weighing 2.5 metric tons and traveling at 90 km/h hits a 500 m long stretch of black
ice. Unfortunately, due to skidding, neither accelerating nor braking has any effect on the
speed! The driver manages to maintain steady straight direction of motion and the only
impact is provided by the ice friction force, which is numerically equal to 4v² Newtons, where
the velocity v of the car is measured in m/sec.
(a) Using Newton's Second Law F = ma, set up a mathematical model for the position
x(t) and velocity v(t) of the car as functions of time t. Start by drawing a diagram and
choosing a consistent system of units based on kg, m, sec (1 ton = 1000 kg, 1 m/sec =
3.6 km/h, 1 N = 1 kg · m/sec²). Introduce and label the variables, show the units and
write down the differential equations and the intial conditions.
(b) Use the model in part a to calculate v(t) and x(t). Fully show the process of solving the
initial value problems.
(c) Based on your work so far, how long will it take to pass the iced over stretch of the road
and how fast will the car be moving as it exits the ice?
Do not use a calculator! Leave your answers in an "algebraic" form, which may involve
exponential functions and logarithms, simplify as appropriate, and clearly specify the
units (e.g. sec, m/sec or km/h).
Transcribed Image Text:A car weighing 2.5 metric tons and traveling at 90 km/h hits a 500 m long stretch of black ice. Unfortunately, due to skidding, neither accelerating nor braking has any effect on the speed! The driver manages to maintain steady straight direction of motion and the only impact is provided by the ice friction force, which is numerically equal to 4v² Newtons, where the velocity v of the car is measured in m/sec. (a) Using Newton's Second Law F = ma, set up a mathematical model for the position x(t) and velocity v(t) of the car as functions of time t. Start by drawing a diagram and choosing a consistent system of units based on kg, m, sec (1 ton = 1000 kg, 1 m/sec = 3.6 km/h, 1 N = 1 kg · m/sec²). Introduce and label the variables, show the units and write down the differential equations and the intial conditions. (b) Use the model in part a to calculate v(t) and x(t). Fully show the process of solving the initial value problems. (c) Based on your work so far, how long will it take to pass the iced over stretch of the road and how fast will the car be moving as it exits the ice? Do not use a calculator! Leave your answers in an "algebraic" form, which may involve exponential functions and logarithms, simplify as appropriate, and clearly specify the units (e.g. sec, m/sec or km/h).
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