Solution_Problem_of_the_Week_&acirc;€“_9

# Solution_Problem_of_the_Week_&acirc;€“_9 - v ave =...

This preview shows page 1. Sign up to view the full content.

Solution Problem of the Week – 9 An automobile of mass 1500 kg accelerates from rest to 20 m/s in 5 seconds. Neglect air resistance. Assume the wheels do not slip on the pavement, which means that the velocity of atoms when they are in contact with the road (at the bottom of the wheel) is always zero. (This is similar to the case of walking or running without slipping; there’s no displacement at the point of contact.) (a) What is the average horizontal component of the force that the road exerts on the wheels (total force on all four wheels, not the force on one wheel)? ! ! p ! t = m ! ! v ! t = 1500 " 20 m / s 5 s = 6000 kg " m / s 2 , ! F = ! ! p ! t = 6000 N (b) In the point-particle analysis of this situation, what is the work done by this force? W = ! KE trans = 1 2 mv 2 = 3 " 10 5 J (c) How far does the automobile travel in the 5 seconds? Assuming that the car’s acceleration is constant:
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ! v ave = 10 m / s , ! x = ! v ave ! t = 50 m (d) For the real system, how much work is done by the force of the road on the wheels? The force of the road on the wheels does no work on the real system since the points of contact between the tires and the road are not displaced by the friction force. (e) For the real system, label which of the following types of energy increase or decrease over the 5 second period: translational kinetic energy, rotational kinetic energy, thermal energy, chemical energy. Increase: translational KE, rotational KE, thermal energy. Decrease: chemical energy. (f) For any of the energies that you identified in (e) as decreasing, what is the minimum magnitude it can have decreased by? The chemical energy must decrease by at least 3 x 10 5 J....
View Full Document

## This note was uploaded on 12/07/2011 for the course PHYS 172 taught by Professor ? during the Fall '08 term at Purdue.

Ask a homework question - tutors are online