2nd Exam Lec

A ball is thrown vertically upward from the surface of the earth. Consider the following quantities:

(1) the speed of the ball;

(2) the velocity of the ball;

(3) the acceleration of the ball.

Which of these is/are zero when the ball has reached the maximum height?

• 1 and 2 only

• 1 only

• 1,2, and 3

• 1 and 3 only

A bus travels the 100 miles between A and B at 50 mi/h and then another 100 miles between B and C at 70 mi/h. The average speed of the bus for the entire 200-mile trip is:

• more than 60 mi/h

• equal 60 mi/h

• less than 60 mi/h

• insufficient information

A locomotive is accelerating at 1.6 m/s². It passes through a 20 m-wide crossing in a time of 2.4 s. After the locomotive leaves the crossing, how much time is required until its speed reaches 32 m/s?

• 10.25 s

• 13.60 s

• 21.3 s

• 27.90 s

For which of the following situations will the path length equal the magnitude of displacement?

• A jogger is running around a circular path.

• A ball is rolling down an inclined plane

• A train travels 5 miles east before it stops. It then travels 2 miles west.

• A ball rises and falls after being thrown straight up from the earth's surface.

A rock is thrown downward with an initial speed of 2.0 m/s. What is the speed of the rock after it has descended 2.0 m?

• 5.93 m/s

• 6.57 m/s

• 39.2 m/s

• 43.2 m/s

A ball is in free fall. Its acceleration is:

• downward during both ascent and descent

• downward during ascent and upward during descent

• upward during ascent and downward during descent

• downward at all times except at the very top, when it is zero

What makes speed different from velocity?

• different magnitude and same direction

• different direction and same magnitude

• has magnitude only

• has direction only

Which one of the following statements must be true if the expression x =  $v_1$  t + 1/2a $t^2$    is to be used?

• x is constant

• t is constant

• v is constant

• a is constant

In a vacuum tube, a feather is seen to fall as fast as a coin. This is because

• gravity doesn't act in a vacuum.

• greater air resistance acts on the coin.

• gravity is greater in vacuum.

• air resistance doesn't act in a vacuum

Without air resistance, the time for a vertically tossed ball to return to where it was thrown is

• the same as the time going up

• less than the time going upward

• more than the time going upward

• 9.8 m/s for every second in the air