All AP Physics C: Mechanics Resources
Example Questions
Example Question #1 :Calculating Motion In Two Dimensions
Aball is thrown horizontally from the top of ahigh building. It has an initial velocity ofand lands on the groundaway from the base of the building. Assuming air resistance is negligible, which of the following changes would cause the range of this projectile to increase?
I. Increasing the initial horizontal velocity
II. Decreasing the mass of the ball
III. Throwing the ball from an identical building on the moon
II only
I, II, and III
I only
I and II
I and III
I and III
Relevant equations:
选择I is true becauseis proportional to the range, so increasingincreasesifis constant. This relationship is given by the equation:
选择II is false because the motion of a projectile is independent of mass.
选择III is true because the vertical acceleration on the moonwould be less. Decreasingincreases the time the ball is in the air, thereby increasingifis constant. This relationship is also shown in the equation:
Example Question #1 :Calculating Motion In Two Dimensions
Water emerges horizontally from a hole in a tankabove the ground. If the water hits the groundfrom the base of the tank, at what speed is the water emerging from the hole? (Hint: Treat the water droplets as projectiles.)
To understand this problem, we have to understand that the water has a x-velocity and a y-veloctiy. The x-velocity never changes.
First we want to find the time it took for the water to hit the ground. We can use this equation:
We know that the y-velocity is 0 to start with, acceleration isand.
Substituting into the equation, we get:
接下来我们必须把时间代入equation for the x component
We know thatand, so we can conclude that:
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