Question 1

If I throw a rock in a lake at 30° or 60° from horizontal,with the same initial speed,it will splash on the same spot.So what is the difference? Should we only consider angles from 0° to 45°?

Accepted Answer

The answer of If I throw a rock in a...

Question 2

You can launch a projectile with a fixed initial speed but at any angle above the horizontal,and it feels no air resistance.The time for it to return to the ground does not depend on the angle at which you launch it.

Accepted Answer

The time for a projectile to return to the ground depends on the vertical component of its initial velocity, which is affected by the launch angle.

Question 3

You throw a 5.0 kg stone from the top of a cliff with an initial vertical velocity of 8.0 m/s downward and an initial horizontal velocity of 7.0 m/s away from the cliff,and it feels no air resistance.After the stone is in the air but free of your hand,its acceleration remains constant at 9.8 m/s² downward but its speed changes.

Accepted Answer

The stone experiences constant acceleration due to gravity, but its velocity changes as it travels downward and away from the cliff. This change in velocity indicates a change in speed, thus the statement is true.

Question 4

Two bullets are fired simultaneously parallel to a horizontal plane.The bullets have different masses and different initial velocities.Which one will strike the plane first?
A)the fastest one
B)the slowest one
C)the heaviest one
D)the lightest one
E)They strike the plane at the same time.

Accepted Answer

Since the bullets are fired simultaneously parallel to the horizontal plane, they will both experience the same acceleration due to gravity. Therefore, they will both hit the plane at the same time, regardless of their mass or initial velocity.

Question 5

The components of a vector will be the same no matter what coordinate system is used to express that vector.

Accepted Answer

The components of a vector can change depending on the coordinate system used, although the vector itself remains the same.

Question 6

Bob and Biff throw identical rocks off a tall building at the same time.Bob throws his rock straight downward.Biff throws his rock downward and outward such that the angle between the initial velocity of the rock and the horizon is 30 degrees.Biff throws the rock with a speed twice that of Bob's rock.Which rock hits the ground first (assume the ground near the building is flat)?
A)They hit at the same time.
B)Bob's rock
C)Biff's rock
D)Impossible to determine

Accepted Answer

The time it takes for an object to fall to the ground only depends on its vertical component of velocity, not on its horizontal component. Both rocks have the same vertical component of velocity, as they are dropped from the same height (assuming they are released at the same time). Therefore, both rocks hit the ground at the same time. The fact that Biff's rock has a higher initial velocity and a horizontal component does not affect the time it takes to fall to the ground.

Question 7

Which of the following is NOT a vector?
A)speed
B)acceleration
C)velocity
D)displacement

Accepted Answer

Speed is a scalar quantity because it only has magnitude and no direction. The other options (acceleration, velocity, and displacement) are all vector quantities because they have both magnitude and direction.

Question 8

Shown here are the velocity and acceleration vectors for an object in several different types of motion.In which case is the object slowing down and turning to its right?
A)

B)

C)

D)

E)

Accepted Answer

In option B, the velocity vector is to the right and the acceleration vector is downwards, indicating a decrease in speed and a change in direction to the right.

Question 9

A football is kicked toward the goal posts and feels no air resistance.While it is in the air,the only force acting on it is 9.8 m/s² downward due to gravity.

Accepted Answer

The answer of A football is kicked toward the goal...

Question 10

What is the minimum number of vectors (none of which have the same magnitude)for which it is theoretically possible that the sum of those vectors can be equal to zero?

Accepted Answer

The answer of What is the minimum number of vectors...

Question 11

Which of the following ideas is true about projectile motion with no air drag?
A)  +
 = constant.
B)The acceleration is +g when the object is rising and -g when falling.
C)The velocity of the object is zero at the point of maximum elevation.
D)The trajectory will depend on the object's mass as well as its initial velocity and launch angle.
E)The horizontal motion is independent of the vertical motion.

Accepted Answer

The answer of Which of the following ideas is true...

Question 12

Are projectiles subject to constant acceleration in two dimensions?

Accepted Answer

The answer of Are projectiles subject to constant acceleration in...

Question 13

To achieve maximum range of a projectile,for a fixed initial velocity,on Earth we must launch it at 45°.If we were at the moon should we do the same?

Accepted Answer

The answer of To achieve maximum range of a projectile,for...

Question 14

A ball is thrown at an angle above the horizontal from the top of a cliff and feels no air resistance.A runner at the base of the cliff moves horizontally so that she is always under the ball.In this runner's reference frame,the path of the ball is a straight line rather than a parabola.

Accepted Answer

In the runner's reference frame, the ball appears to move horizontally along with the runner. As such, the path of the ball appears to be a straight line rather than a parabola. This is because the vertical motion of the ball is cancelled out by the horizontal motion of the runner. However, in reality, the ball is still following a parabolic path relative to the ground.

Question 15

The sum of the two vectors  and  is equal to zero.What can you conclude about  and  ?

Accepted Answer

The answer of The sum of the two vectors ...

Question 16

Shown here are the velocity and acceleration vectors for an object in several different types of motion.In which case is the object's velocity changing while its speed is not changing?
A)

B)

C)

D)

E)None of these cases

Accepted Answer

The answer of Shown here are the velocity and acceleration...

Question 17

A grasshopper leaps into the air at a 62 degree angle above the horizontal.At its highest point,the grasshopper's velocity and acceleration are equal to zero.

Accepted Answer

At its highest point, the grasshopper's vertical velocity is zero, but its horizontal velocity remains constant, and its acceleration is equal to the acceleration due to gravity, not zero.

Quiz 3: Vectors and Motion in Two Dimensions

If I throw a rock in a lake at 30° or 60° from horizontal,with the same initial speed,it will splash on the same spot.So what is the difference? Should we only consider angles from 0° to 45°?

You can launch a projectile with a fixed initial speed but at any angle above the horizontal,and it feels no air resistance.The time for it to return to the ground does not depend on the angle at which you launch it.

Two bullets are fired simultaneously parallel to a horizontal plane.The bullets have different masses and different initial velocities.Which one will strike the plane first?

The components of a vector will be the same no matter what coordinate system is used to express that vector.

Which of the following is NOT a vector?

Shown here are the velocity and acceleration vectors for an object in several different types of motion.In which case is the object slowing down and turning to its right?

A football is kicked toward the goal posts and feels no air resistance.While it is in the air,the only force acting on it is 9.8 m/s2 downward due to gravity.

What is the minimum number of vectors (none of which have the same magnitude)for which it is theoretically possible that the sum of those vectors can be equal to zero?

Which of the following ideas is true about projectile motion with no air drag?

Are projectiles subject to constant acceleration in two dimensions?

To achieve maximum range of a projectile,for a fixed initial velocity,on Earth we must launch it at 45°.If we were at the moon should we do the same?

A ball is thrown at an angle above the horizontal from the top of a cliff and feels no air resistance.A runner at the base of the cliff moves horizontally so that she is always under the ball.In this runner's reference frame,the path of the ball is a straight line rather than a parabola.

The sum of the two vectors and is equal to zero.What can you conclude about and ?

Shown here are the velocity and acceleration vectors for an object in several different types of motion.In which case is the object's velocity changing while its speed is not changing?

A grasshopper leaps into the air at a 62 degree angle above the horizontal.At its highest point,the grasshopper's velocity and acceleration are equal to zero.

A football is kicked toward the goal posts and feels no air resistance.While it is in the air,the only force acting on it is 9.8 m/s² downward due to gravity.