Q198 · Practice questionComplex unfamiliar1 mark
QUESTION 198
A block has a downhill weight component of and a constant applied force of uphill. While sliding, friction has magnitude . Compare an instant when it slides uphill with a later instant when it slides downhill. Which statement about its acceleration is correct?
(A)
It is uphill at both instants.
(B)
It is downhill at both instants, with three times the magnitude during uphill motion.
(C)
It is downhill during uphill motion and uphill during downhill motion.
(D)
It has the same magnitude and direction at both instants.
WORKED SOLUTION
1 markAnswer B
ANSWER
B. It is downhill at both instants, with three times the magnitude during uphill motion.
Worked solution
Taking uphill positive, while moving uphill . While moving downhill friction reverses: . The mass is unchanged, so both accelerations are downhill, in the magnitude ratio . This comparison concerns sliding instants, not the friction at rest.
Equivalent physically justified methods and consistent equivalent units accepted.
Displayed decimals are model answers; accept appropriate significant figures and consistent rounding from stated constants.
Select B.
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