SAT Subject Physics Practice Question 186: Answer and Explanation
The total force acting on an object as a function of time is given in the graph above. What is the magnitude of the change in momentum of the object between t = 0 and t = 0.4 sec?
A. 2 kg-m/sec
B. 5 kg-m/sec
C. 10 kg-m/sec
D. 12 kg-m/sec
E. 15 kg-m/sec
Correct Answer: E
The impulse-momentum theorem says that the change in momentum is equal to the impulse, which is the area under the force versus time graph. The region under the graph from t = 0 to t = 0.4 sec is composed of a right triangle (from t = 0 to t = 0.2 sec) plus a rectangle (from t = 0.2 sec to t = 0.4 sec), so the total area under the graph from t = 0 to t = 0.4 sec is (1/2)(0.2)(100) + (0.4 – 0.2)(25) = 10 + 5 = 15 kg-m/sec.