Ch. 3 Check Your Understanding Flashcards
Suppose you are driving due east, traveling a distance of 1500m in 2 minutes. You then turn due north and travel the same distance in the same time. What can be said about the average speeds and the average velocities for the two segments of the trip?
The average speeds are the same, but the average velocities are different.
A power boat, starting from rest, maintains a constant acceleration. After a certain time t, it’s displacement and velocity are ->r and ->v. At time 2t, what would be its displacement and velocity, assuming the acceleration remains the same?
4->r and 2->v
An object is thrown upward at an angle theta above the ground, eventually retuning to earth.
A) is there any place along the trajectory where the velocity and acceleration are perpendicular? Is so, where?
B) is there any place where the velocity and acceleration are parallel? If so, where?
A) yes, when the object is at its highest point
B) no
Is the acceleration of a projectile equal to zero when the projectile reaches the top of its trajectory?
No
In baseball, the pitchers mound is raised to compensate for the fact that the ball falls downward as it travels from the pitcher toward the batter. If baseball were played on the moon, would the pitchers mound have to be a) higher than, b) lower than, or c) the same height as it is on earth?
B) lower than
A tennis ball is hit upward into the air and moves along an arc. Neglecting air resistance, where along the arc is the speed of the ball a) a minimum and b) a maximum?
A) when the ball is at its highest point in the trajectory
B) at the initial and final positions of the motion
A wrench is accidentally dropped from the top of the mast on a sailboat. Air resistance is negligible. Will the wrench hit at the same place on the deck whether the sailboat is at rest or moving with a constant velocity?
Yes
A rifle, at a height H above the ground, fires a bullet parallel to the ground. At the same instant and at the same height, a second bullet is dropped from rest. In the absence of air resistance, which bullet, if either, strikes the ground first?
Both bullets reach the ground at the same time
A stone is thrown horizontally from the top of a cliff and eventually hits the ground below. A second stone is dropped from rest from the same cliff, falls through the same height, and also hits the ground below. Ignore air resistance. Is each of the following quantities different or the same in the two cases?
A) displacement
B) speed just before impact with the ground
C) time of flight
A) the displacement is greater for the stone thrown horizontally
B) the impact speed is greater for the stone thrown horizontally
C) the time of flight is the same for both stones
A leopard springs upward at a 45 degree angle and then falls back to the ground. Air resistance is negligible. Does the leopard, at any point on its trajectory, ever have a speed that is one-half its initial value?
No
Two balls are launched upward from the same spot at different angles with respect to the ground. Both balls rise to the same maximum height. Ball A, however, follows a trajectory that has a greater range than that of ball B. Ignoring air resistance, decide which ball, if either, has the greater launch speed.
Ball A has the greater launch speed
On a riverboat cruise, a plastic bottle is accidentally dropped overboard. A passenger on the boat estimates that the boat pulls ahead of the bottle by 5 meters each second. Is it possibly to conclude that the magnitude of the velocity of the boat with respect to the shore is 5m/s?
No
A plane takes off at St. Louis, flies straight to Denver, and then returns the same way. The plane flies at the same speed with respect to the ground during the entire flight, and there are no head winds or rail winds. Since the earth revolves around its axis once a day, you might expect that the times for the outbound trip and the return trip differ, depending on whether the plane flies against the earths rotation or with it. Is this true, or are the two times the same?
The two times are the same
A child is playing on the floor of a recreational vehicle (RV) as it moves along the highway at a constant velocity. He has a toy cannon, which shoots a marble at a fixed angle and speed with respect to the floor. The cannon can be aimed toward the front or the rear of the RV. Is the range toward be front the same as, less than, or greater than the range toward the rear?
A) from the child’s point of view
B) from the point of view of an observer standing still on the ground
A) the range toward the front is the same as the range toward the rear
B) the range toward the front is greater than the range toward the rear
Three swimmers can swim equally fast relative to the water. They have a race to see who can swim across a river in the least time. Swimmer A swims perpendicular to the current and lands on the far shore downstream, because the current has swept him in that direction. Swimmer B swims upstream at an angle to the current, choosing the angle so that he lands on the far shore directly opposite of the starting point. Swimmer C swims downstream at an angle to the current in an attempt to take advantage of the current. Who crosses the river in the least time?
Swimmer A
