Carol eats a regular hamburger and drinks a glass of cow's milk for breakfast. Suppose that energy content of the hamburger and the milk are 2115 kJ and 565kJ respectively. What % of energy from the food does Carol use to push a sack of rice along a horizontal distance of 4.75 m? Her hands exerted a force of 50N applied 20° down with the horizontal.

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19 March 2017

Draw a diagram! It's not clear from the way the question is written, whether the force she is exerting makes a 20* angle with the horizontal but I think that is what is meant. You need to work out the proportion of the force applied that is working horizontally - using Pythagorus. Then you can work out the "work done" and divide that by the total input energy to get a proportion of the food energy used in this exercise. Hope that helps.

19 March 2017

Assuming that the question means that her force is applied 20 degrees below the vertical, resolve this force. Use work done = force x distance moved in the direction of the force to calculate work done in pushing the rice. Then express this as a percentage of the total energy in. I make the answer 0.008%.

19 March 2017

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