# Year 11 Physics assignment. General help.

1. Jun 16, 2012

### bartrocs

1. The problem statement, all variables and given/known data

A car of mass 1600kg is allegedly travelling at 60Km/h and an explosion breaks it into 3 pieces. One of the pieces contained the driver and had the brakes still functioning. The piece containing the driver left a skid mark 4.33 meters long and the coefficient of friction between the tires and the road was 0.7. One piece of wreckage had a mass of 700kg and headed north at a speed of 76.62 m/s. Another piece had a mass of 400kg and headed S40°W at a speed of 7.5m/s. The piece containing the driver had a mass of 500kg and headed S30°E. Evaluate the physics of the evidence provided.

3. The attempt at a solution

We found the speed of the piece of wreckage containing the driver to have a velocity of 7.71345 m/s and the sum of the momentum of each of the pieces to be 47995.9 kg m/s. if the driver was travelling at 60km/h, then the momentum of the car would have been 26666.7kg m/s not 47995.9kg m/s. We then worked out the speed of the car before the explosion was 29.997 m/s. Therefore the driver was speeding. We worked out the Kinetic Energy for each piece of the wreckage and the Kinetic energy of the car travelling at 29.997m/s. Since KE before = KE after, we found that if the driver was travelling at 29.997m/s, then additional energy of 1360968.3 joules would have to be added by the explosion. Is this correct? Also, we concluded that if the driver was traveling at his alleged 60km/h (16.667m/s), then additional energy of 1858621.3 joules in order to maintain the law of conservation of energy and momentum. Is this correct? Please help, as I do not know if we are follow the correct reasoning for this project.