A woman riding on a bus suspends a ball of mass m from the ceiling using a massless string while the bus is moving at constant speed on a horizontal road. When the bus is accelerating, with its engine off, down a hill inclined downward with a slope s, what is the change of the angle at which the ball is suspended as observed by the woman on the bus?
a) 0
b) tan−1s to the front of the bus
c) tan−1s to the back of the bus
d) sin−1s to the front of the bus
e) sin−1s to the back of the bus
f) not enough information