A 1500 kg car skids to a halt on a wet road where . How fast was the car traveling if it leaves -long skid marks?
The speed of the car at the moment it skidded is
Velocity is a mechanical number that indicates the change in distance of an object in unit time in a specified direction. The metric unit is the meter per second. It explains how the thing moves.
Using Newton's second law
Here, is the gravitational force, is the mass, is the acceleration.
Substitute the values, where
To find acceleration we use
The initial velocity , here
Seat belts and air bags save lives by reducing the forces exerted on the driver and passengers in an automobile collision. Cars are designed with a “crumple zone” in the front of the car. In the event of an impact, the passenger compartment decelerates over a distance of about 1 m as the front of the car crumples. An occupant restrained by seat belts and air bags decelerates with the car. By contrast, an unrestrained occupant keeps moving forward with no loss of speed (Newton’s first law!) until hitting the dashboard or windshield. These are unyielding surfaces, and the unfortunate occupant then decelerates over a distance of only about 5 mm.
a. A 60 kg person is in a head-on collision. The car’s speed at impact is 15 m/s. Estimate the net force on the person if he or she is wearing a seat belt and if the air bag deploys.
b. Estimate the net force that ultimately stops the person if he or she is not restrained by a seat belt or air bag.
Suppose you push a hockey puck of mass m across frictionless ice for 1.0 s, starting from rest, giving the puck speed v after traveling distance d. If you repeat the experiment with a puck of mass 2m, pushing with the same force, a. How long will you have to push for the puck to reach the same speed v?
b. How long will you have to push for the puck to travel the same distance d?
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