AP Physics 1 Question 204: Answer and Explanation
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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
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 = (Fw/g)a, you get 10 N = [(20 N)/(10 m/s2)]a, which gives a = 5 m/s2.