Starting from rest, a car accelerates down a straight road with constant acceleration a for a time t, then the direction of the acceleration is reversed, i.e., it is -a, and the car comes to a stop in an additional time t, the time for the whole trip being 2t. At what time, or times, is the average velocity of the car for the trip equal to its instantaneous velocity during the trip?
a. There is no such time.
b. It is at the halfway point at t.
c. This occurs at 2 times, at 0.5 t and 1.5 t.
d. This occurs at 2 times, at 0.707 t and 1.293 t.
[Ques. 2] Starting from rest, a car accelerates down a straight road with constant acceleration a1 for a time t1, then the acceleration is changed to a different constant value a2 for an additional time t2 . The total elapsed time is t1 + t2 . Can the equations for motion with constant acceleration be used to find the total distance traveled?
a. No, because this is not a case of constant acceleration.
b. Yes, use (a1 + a2)/2 as the average acceleration and the total time in the calculation.
c. Yes, use a1 + a2 as the acceleration and the average time (t1 + t2)/2 in the calculation.
d. Yes, break the problem up into 2 problems, one with the conditions for the first time interval and the other with the conditions for the second time interval, noting that for the second time interval the initial velocity is that from the end of the first time interval. When done, add the distances from each of the time intervals.
[Ques. 3] A thrown stone hits a window but doesn't break it. Instead, it reverses direction and ends up on the ground below the window. In this case, we know:
a. the force of the stone on the glass > the force of the glass on the stone.
b. the force of the stone on the glass = the force of the glass on the stone.
c. the force of the stone on the glass < the force of the glass on the stone.
d. the stone didn't slow down as it hit the glass.
[Ques. 4] An airplane of mass 1.2 104 kg tows a glider of mass 0.6 104 kg. The airplane propellers provide a net forward thrust of 5.4 104 N. What is the glider's acceleration?
a. 2.0 m/s2
c. 6.0 m/s2
b. 3.0 m/s2
d. 9.8 m/s2
[Ques. 5] The statement by Newton that for every action there is an opposite but equal reaction is regarded as which of his laws of motion?
a. first
c. third
b. second
d. fourth
[Ques. 6] An automobile of mass 2000 kg moving at 20 m/s is braked suddenly with a constant braking force of 10,000 N. How far does the car travel before stopping?
a. 40 m
c. 120 m
b. 80 m
d. 160 m
[Ques. 7] If we know that a nonzero net force is acting on an object, which of the following must we assume regarding the object's condition? The object is:
a. at rest.
c. being accelerated. b. moving with a constant velocity.
d. losing mass.
[Ques. 8] Two forces act on a 6.00-kg object. One of the forces is 11.0 N. If the object accelerates at 2.00 m/s2, what is the greatest possible magnitude of the other force?
a. 33.0 N
c. 3.0 N
b. 23.0 N
d. 1.0 N
[Ques. 9] An astronaut applies a force of 500 N to an asteroid, and it accelerates at 3.00 m/s2 . What is the asteroid's mass?
a. 1500 kg
c. 600 kg
b. 135 kg
d. 167 kg
[Ques. 10] A 7.0-kg bowling ball experiences a net force of 6.0 N. What will be its acceleration?
a. 0.86 m/s2
c. 7.0 m/s2
b. 6.0 m/s2
d. 42 m/s2
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