Answer to Question #197973 in General Chemistry for Riane

Question

A 100-kg body moving at 35 kph was found to have a total energy of 570 J. How much potential energy was there in the moving body?

a. 84 J

b. 490 J

c. 1.1 kJ

d. 55 J

Answer 1

The energy is conserved, which means that the sum of a single body's kinetic and potential energies remains constant. Thus, we calculate the potential energy using the equation for the kinetic energy and the proper conversions (since we have the velocity in kph):

$E_T = E_{potential} + E_{kinetic}$

$E_{potential} = E_T - E_{kinetic} \, = E_{kinetic} - \frac{1}{2}mv^2 \,$

$E_{potential} = 570\,J - (\frac{100\,kg}{2})[(35\frac{km}{h})(\frac{1\,h}{3600\,s})(\frac{1000\,m}{1\,km})]^2$

$E_{potential} = [570 - (50)(\frac{350}{36})^2]\,J = [570 - 4726]\,J = -4156\,J$

I didn't reach an answer that matches the options given, I found the potential energy for the moving body to be E_potential = - 4156 J.

References

• Ed. by J. J. Lagowski. (2004) Chemistry: Foundations and Applications. New York: Macmillan.