heikediguore

Following some advice on another forum, I decided to take the following approach: 1. Assuming constant acceleration, with known initial and final velocities, use an equation of motion to find the acceleration. 2. Apply the acceleration to the work(force,distance) equation to find the energy requirement for such an acceleration over the given distance. Here's what I got: Equation of motion taken from wikipedia "Equations of Motion": Vf^2= Vi^2 + 2ad 17 (m/s)^2 = 0 + 2a * 5000 m 289 (m/s)^2 = (10,000 m)a so a=2.89 * 10^-2 m/s^2 W=Fd=mad =1000 kg * 2.89 * 10^-2 m/s^2 * 5000 m =1.45 * 10^5 kg (m/s)^2 =1.45 * 10^5 j 1 Snickers bar = 273 kcal =2.73 * 10^5 cal cal/4.184 = joules (2.73*10^5 cal)/4.184 =6.52 * 10^4 j/snickers so, using the Fd energy result: (1.45 * 10^5 j)/(6.52 * 10^4 j/snickers) =94.5 Snickers bars

I thought I included acceleration by figuring out the change in energy. No? Ok, for simplicity's sake, so I don't have to calculate every force from friction to turbulence to gravity to nuclear decay, I'll say that the vehicle undergoes constant acceleration during its trip, such that the initial velocity is 0 m/s and the final velocity is 17 m/s. I was trying to find a formula for calculating total energy consumption, and I thought that I could do that by constructing power in terms of energy and time and then putting in a value for time. I know I need to integrate something here. Is it: integral[0,17](E(v)dv) where E(v)=kinetic energy and v=velocity so: integral[0,17](1/2mv^2)dv =[0,17](1/2mv^3)/3 =[0,17](mv^3)/6 =1000kg*(17 m/s)^3 - 0 =1000kg*4913 (m/s)^3 =4.913 * 10^6 kg (m/s)^3 Now I don't know what to do.

I wanted to find out how much food energy it would take to run a car. Thought experiment: Starting from a stop, a 1000 kg car goes 5 km in 5 min. How many 2 oz. Snickers bars does it take to provide this energy? 5 min. = 300 s 5 km = 5000 m so velocity = ~17 m/s Energy = E(final) - E(initial) = (1/2 * mv^2) - 0 = 1/2*(1000 kg)(17 m/s)^2 = 289,000 kg (m/s)^2 = 289,000 j so power requirement is: 289,000 j/s =289,000 W sustained over 300 sec, Energy = power * time =289,000 W * 300 s =8.67 * 10^7 j 1 calorie = 4.184 joules (8.67 * 10^7 j)/(4.184 j/cal) =2.07 * 10^7 cal 1000 cal = 1 kcal (2.07 * 10^7 cal)/(1000 cal/kcal) =2.07 * 10^4 kcal 1 Snickers bar = 273 kcal (see http://www.thecaloriecounter.com/Foods/1900/19155/1/Food.aspx) 2.07 * 10^4 kcal/(273 kcal/Snickers) =75.8 Snickers bars Is that correct?