physics quiz 2

For general projectile motion with no air resistance, the vertical component of a projectile's acceleration A. remains a non-zero constant. B. continuously increases. C. first decreases and then increases. D. is always zero. E. continuously decreases.

A. remains a non-zero constant.

James and John dive from an overhang into the lake below. James simply drops straight down from the edge. John takes a running start and jumps with an initial horizontal velocity of 25 m/s. If there is no air resistance, when they reach the lake below Select one: A. the splashdown speed of John is larger than that of James. B. they will both have the same splashdown speed. C. the splashdown speed of John must be 25 m/s larger than that of James. D. the splashdown speed of James is larger than that of John. E. the splashdown speed of James must be 9.8 m/s larger than that of John.

A. the splashdown speed of John is larger than that of James.

A ball is thrown with an initial velocity of 20 m/s at an angle of 60° above the horizontal. If we can neglect air resistance, what is the horizontal component of its instantaneous velocity at the exact top of its trajectory? Select one: A. 17 m/s B. 10 m/s C. 20 m/s D. zero

B. 10 m/s

A hockey puck slides off the edge of a platform with an initial velocity of 20 m/s horizontally. The height of the platform above the ground is 2.0 m. What is the magnitude of the velocity of the puck just before it touches the ground? You can neglect air resistance. Select one: A. 6.3 m/s B. 21 m/s C. 22 m/s D. 24 m/s E. 25 m/s

B. 21 m/s

A ball thrown horizontally from a point 24 m above the ground, strikes the ground after traveling horizontally a distance of 18 m. With what speed was it thrown, assuming negligible air resistance? Select one: A. 7.4 m/s B. 8.1 m/s C. 6.1 m/s D. 8.9 m/s

B. 8.1 m/s

A stone is thrown horizontally with an initial speed of 10 m/s from the edge of a cliff. A stopwatch measures the stone's trajectory time from the top of the cliff to the bottom to be 4.3 s. What is the height of the cliff if air resistance is negligibly small? Select one: A. 77 m B. 91 m C. 43 m D. 22 m

B. 91 m

Mary and Debra stand on a snow-covered roof. They both throw snowballs with the same initial speed, but in different directions. Mary throws her snowball downward, at 30° below the horizontal; Debra throws her snowball upward, at 30° above the horizontal. Which of the following statements are true about just as the snowballs reach the ground below? (There could be more than one correct choice.) Select one or more: A. Both snowballs hit the ground at the same time. B. Both snowballs will hit the ground with the same speed. C. Mary's snowball reaches the ground before Debra's snowball. D. Mary's snowball will have a higher speed than Debra's snowball. E. Debra's snowball will have a higher speed than Mary's snowball.

B. Both snowballs will hit the ground with the same speed. C. Mary's snowball reaches the ground before Debra's snowball.

Mary and Debra stand on a snow-covered roof. They both throw snowballs with the same initial speed, but in different directions. Mary throws her snowball downward, at 30° below the horizontal; Debra throws her snowball upward, at 30° above the horizontal. Which of the following statements are true about just before the snowballs reach the ground below? (There could be more than one correct choice.) Select one or more: A. Both snowballs will take the same amount of time to hit the ground. B. Debra's snowball will stay in the air longer than Mary's snowball. C. Mary's snowball has a greater downward acceleration than Debra's snowball. D. Debra's snowball has exactly the same acceleration as Mary's snowball. E. Mary's snowball will stay in the air longer than Debra's snowball.

B. Debra's snowball will stay in the air longer than Mary's snowball. D. Debra's snowball has exactly the same acceleration as Mary's snowball.

In an air-free chamber, a pebble is thrown horizontally, and at the same instant a second pebble is dropped from the same height. Compare the times of fall of the two pebbles. Select one: A. The thrown pebble hits first. B. They hit at the same time. C. The dropped pebble hits first. D. We cannot tell without knowing which pebble is heavier.

B. They hit at the same time.

For general projectile motion with no air resistance, the horizontal component of a projectile's acceleration A. continuously decreases. B. is always zero. C. first decreases and then increases. D. remains a non-zero constant. E. continuously increases.

B. is always zero.

For general projectile motion with no air resistance, the horizontal component of a projectile's velocity A. remains zero. B. remains a non-zero constant. C. continuously increases. D. first decreases and then increases. E. continuously decreases.

B. remains a non-zero constant.

A boy throws a rock with an initial velocity of at 30.0° above the horizontal. How long does it take for the rock to reach the maximum height of its trajectory if air resistance is negligibly small and g = 9.80 m/s2? Select one: A. 0.313 s B. 0.441 s C. 0.160 s D. 0.282 s

C. 0.160 s

A plane flying horizontally at a speed of 50 m/s and at an elevation of 160 m drops a package, and 2.0 s later it drops a second package. How far apart will the two packages land on the ground if air resistance is negligible? Select one: A. 160 m B. 320 m C. 100 m D. 180 m

C. 100 m

Which of the following statements are true about an object in two-dimensional projectile motion with no air resistance? (There could be more than one correct choice.) Select one: A. The speed of the object is constant but its velocity is not constant. B. The speed of the object is zero at its highest point. C. The horizontal acceleration is always zero and the vertical acceleration is always a non-zero constant downward. D. The acceleration of the object is +g when the object is rising and -g when it is falling. E. The acceleration of the object is zero at its highest point.

C. The horizontal acceleration is always zero and the vertical acceleration is always a non-zero constant downward.

A ball is thrown horizontally from the top of a tower at the same instant that a stone is dropped vertically. Which object is traveling faster when it hits the level ground below if neither of them experiences any air resistance? Select one: A. It is impossible to tell because we do not know their masses. B. the stone C. the ball D. Both are traveling at the same speed.

C. the ball

A football kicker is attempting a field goal from out. The ball is kicked and just clears the lower bar with a time of flight of 2.9 s If the angle of the kick was 45°, what was the initial speed of the ball, assuming no air resistance? Select one: A. 19.7 m/s B. 39 m/s C. 2.2 m/s D. 21.5 m/s

D. 21.5 m/s

A rock is thrown from the upper edge of a tall cliff at some angle above the horizontal. It reaches its highest point and starts falling down. Which of the following statements about the rock's motion are true just before it hits the ground? (There could be more than one correct choice.) Select one: A. Its horizontal velocity component is zero. B. Its speed is the same as it was just as it was launched. C. Its velocity is vertical. D. Its horizontal velocity component is the same as it was just as it was launched. E. Its vertical velocity component is the same as it was just as it was launched.

D. Its horizontal velocity component is the same as it was just as it was launched.

James and John dive from an overhang into the lake below. James simply drops straight down from the edge. John takes a running start and jumps with an initial horizontal velocity of 25 m/s. Compare the time it takes each to reach the lake below if there is no air resistance. Select one: A. John reaches the surface of the lake first. B. Cannot be determined without knowing the weight of both James and John. C. James reaches the surface of the lake first. D. James and John will reach the surface of the lake at the same time. E. Cannot be determined without knowing the mass of both James and John.

D. James and John will reach the surface of the lake at the same time.

A pilot drops a package from a plane flying horizontally at a constant speed. Neglecting air resistance, when the package hits the ground the horizontal location of the plane will Select one: A. be behind the package. B. depend on the speed of the plane when the package was released. C. be in front of the package. D. be directly over the package.

D. be directly over the package.

A player kicks a soccer ball in a high arc toward the opponent's goal. At the highest point in its trajectory Select one: A. the ball's acceleration is zero but its velocity is not zero. B. both the velocity and the acceleration of the soccer ball are zero. C. the ball's velocity points downward. D. neither the ball's velocity nor its acceleration are zero. E. the ball's acceleration points upward.

D. neither the ball's velocity nor its acceleration are zero.