Problem on Kinetic Friction

Robertoalva

1. A police officer investigating an accident estimates from the damage done that a moving car hit a stationary car at 25 km/h. If the moving car left skid marks 44 m long, and if the coefficient of kinetic friction is 0.68, what was the initial speed of the moving car?

2. Homework Equations
fk = μk N

F = ma
3. The Attempt at a Solution
drew a free body diagram, converted 25 km/h to 6.94 m/s

Related Introductory Physics Homework Help News on Phys.org

haruspex

Homework Helper
Gold Member
2018 Award
Can you calculate the deceleration of the skidding car?

Robertoalva

i tried and i do not know how. i tried getting the time by multiplying some number bye 44 in order to give me 6.94 but I didn't get the exact number... it is approaching to 6.3something.

ap123

Apply Newton 2 to your free-body diagram to get the acceleration of the car.
Then you can calculate the initial velocity.

Andrew Mason

Homework Helper
1. A police officer investigating an accident estimates from the damage done that a moving car hit a stationary car at 25 km/h. If the moving car left skid marks 44 m long, and if the coefficient of kinetic friction is 0.68, what was the initial speed of the moving car?

2. Homework Equations
fk = μk N

F = ma
3. The Attempt at a Solution
drew a free body diagram, converted 25 km/h to 6.94 m/s
How is the change in kinetic energy of the car (ie. from just before the skid starts until it strikes the car) related to the length of the skid mark and the force of friction?

AM

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving