# Down the Hill Lab Report

Name: Corinne Chen Block: 1 β 3 Date: May 22nd, 2013 Purpose: To investigate and compare the potential energy, kinetic energy and speed of a cart on a hill 1 kg h 1 m Materials: 1. 2. Cart & 1 kg mass 3. Board 4. Timer 5. Metre ruler 6. Tape Data Table: With 1 kg mass: Trial #| Distance(m)| Time(s)| 1| 1m| 0. 41s| 2| 1m| 0. 45s| 3| 1m| 0. 44s| Without 1 kg mass: Trial #| Distance(m)| Time(s)| 1| 1m| 0. 42s| 2| 1m| 0. 48s| 3| 1m| 0. 45s| Calculations: With 1 kg mass: Average time = 0. 333s Average velocity = Distance ? Average time = 1m ? 0. 4333s ? 2. 308m/s Total mass = (7. 5N ? 9. 8N/kg) + 1kg ? 1. 765kg Height = 0. 33m Kinetic energy = ? mv2 = ? ? 1. 765kg ? (2. 308m/s)2 ? 4. 70J Potential energy = mgh = 1. 765kg ? 9. 8N/kg ? 0. 33m = 5. 71J Without 1 kg mass: Average time = 0. 45s Average velocity = Distance ? Average time = 1m ? 0. 45s ? 2. 236m/s Mass = 7. 5N ? 9. 8N/kg ? 0. 765kg Height = 0. 33m Kinetic energy = ? mv2 = ? ? 0. 765kg ? (2. 236/s)2 ? 1. 91J Potential energy = mgh = 0. 765kg ? 9. N/kg ? 0. 33m = 2. 47J Analysis Questions: How did the potential and kinetic energy compare (top and bottom of the hill)? Explain using law of conservation of energy.

(use values of KE and PE for cart with mass attached) According to the law of conservation of energy, in an isolated system, the initial potential energy and the kinetic energy should be the same. However, when we were doing the experiment, we could not guarantee for ideal situation with no extra resistance, so the data above, which shows that there is difference between the two energies (?

ME = 1. 01J), indicates a certain amount of the loss of energy when the cart was running. The loss of energy was used to overcome the resistance. Furthermore, the less the experimental errors are, the closer the numbers of the two energies will be. What happened to the PE, KE and speed once you removed the 1 kg mass? (compare all values with and without the mass) The speed almost remained the same (2. 308m/s & 2. 236m/s), while PE & KE nearly halved after we removed the 1 kg mass (PE: 5. 71J & 2. 47J and KE: 4. 70J & 1. 91J).

The soap box derby is a race between two carts as they roll down a hill. Does the weight of the cart make much different? Yes, it does. According to the law of conservation of energy, the kinetic energy equals to the initial potential energy (PE=mgh); while as the height doesnβt change, the amount of the potential energy depends on how much the mass is. As the data shows, when the mass of the cart changed, the potential energy and the kinetic energy also changed. And the ratio of the two masses equals to the ratio of the changing KE/PE.