SAT Subject Physics Practice Question 28: Answer and Explanation
5. While a person lifts a book of mass 2 kg from the floor to a tabletop, 1.5 m above the floor, how much work does the gravitational force do on the book?
A. –30 J
B. –15 J
C. 0 J
D. 15 J
E. 30 J
Correct Answer: A
The gravitational force points downward while the book’s displacement is upward. Therefore, the work done by gravity is –mgh = –(2 kg)(10 N/kg)(1.5 m) = –30 J.