SAT Subject Physics Practice Question 13: Answer and Explanation
4. A 20 N block is being pushed across a horizontal table by an 18 N force. If the coefficient of kinetic friction between the block and the table is 0.4, find the acceleration of the block.
A. 0.5 m/s2
B. 1 m/s2
C. 5 m/s2
D. 7.5 m/s2
E. 9 m/s2
Correct Answer: C
The net force on the block is F – Ff = F – μkFN = F –μkFw = (18 N) – (0.4)(20 N) = 10 N. Since Fnet = ma = ()a, we find that 10 N = a, which gives a = 5 m/s2.