chapter 3

a batter hits a pop fly straight up. A) is the acceleration of the ball on the way up different from its acceleration on the way down? B) is the acceleration of the ball at the top of its flight different from its acceleration just before it lands?

A) no the acceleration is not different because of free fall B) No, the acceleration of the ball is 9.81 m/s2 downward at every point during its flight

what does the intercept of a p-t graph represent? what does the initial slope represent? Assume motion with constant acceleration

at t=0 the intercept represents the initial position of the object. the initial slope of a p-t graph for an object that undergoes constant acceleration is the initial velocity of the object

an object moves with a constant, negative acceleration. Whats the shape of the p-t graph?

downward curvature, parabola

The brakes on a train create a constant deceleration, regardless of how fast it's moving. If the speed of the train is doubled, how does this affect the time required for it to come to a stop?

if the initial speed of the train is doubled, the time required for it to stop will double as well

an object moves with a constant acceleration. What is the shape of its v-t graph

it has a linear velocity-time graph because it changes its velocity by the same amount for equal time intervals

what is the acceleration of an object whose p-t is a straight line? explain

it has zero curvature then we conclude that it has zero acceleration. Its velocity, the slope of the position-time graph, is not changing with time.

sketch a v-t graph for an object whose initial velocity is negative, but whose acceleration is positive

it will have a negative intercept (initial v velocity) but a positive slope (acceleration)

an object is dropped at t=0 and allowed to fall freely toward the ground. Is the distance covered by the object between t=0 and t=1s greater than, less than, or equal to the distance covered by the object between t=1s and t=2s? explain

the distance the object travels between the two times is less than because distance increases with time squared.

an object has a p-t graph that is a straight line with a negative slope. Is the acceleration of this object positive, negative, or zero? Explain

the object is traveling with a constant, negative velocity. Any acceleration would produce a curvature to the position-time graph. Because the graph is a straight line the acceleration must be zero.

can an object that is moving upward be in free fall?

yes, a ball that is thrown upward, under conditions where air friction is negligible, is still described as being in free fall because its motion os influenced only by gravity

if the velocity of a ball is positive, can its acceleration be negative? Give an example if your answer is yes; explain why not if your answer is no

yes. For example, if a ball is thrown straight upward, during the upward journey it has an upward velocity (we'll call upward the positive direction) and a downward acceleration of -9.81 m/s2.

If the velocity of a ball is zero at a given instant of time, can its acceleration at that instant be positive? Give an example if your answer is yes; explain why not if your answer is no

yes. If a ball is thrown straight upward, it momentarily comes to rest while still accelerating at 9.81 m/s2 downwards