A car is stopped at a stoplight. When the light turns green and the car begins t
ID: 1619293 • Letter: A
Question
A car is stopped at a stoplight. When the light turns green and the car begins to accelerate,you notice that a leaf (mass m) is at rest on the front of the car; assume the front of the car is vertical. What is the acceleration of the car so that the leaf just remains at rest with respect to the car i.e., if the leaf is just about to slide? The coecients of frictionbetween the leaf and the car are µs and µk. Assume air resistance is negligible.
A) g
(B) µkg
(C) µsg
(D) gµs
(E) gµk
I know the answer is D, could you please explain why?
Explanation / Answer
The psuedo force on the leaf in opposite direction of motion of the car is,
F=m*a a is the acceleration of the car
if the leaf is at rest, this force is equal to the friction force.
f = F
us*N= m*a
us*mg= m*a
a= us*g
hence, the correct option is D.
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