Question 1

A ball is thrown at an angle of θ above the horizontal. If there is no acceleration due to gravity the ball will follow a straight-line path.

Accepted Answer

If there is no acceleration due to gravity, the ball will not be pulled down towards the earth and will travel in a straight line. The angle at which it was thrown will only affect the direction of the straight-line path.

Question 2

A projectile is launched from ground level with a certain speed. For any range less than the maximum range there are two possible launch angles that give the same range.

Accepted Answer

According to the range equation for a projectile, there are two possible launch angles that give the same range. This is because the range is symmetric about the angle of 45 degrees. Therefore, for any range less than the maximum range, there will be two launch angles that produce that range.

Question 3

Two objects are thrown vertically upwards simultaneously, one on the surface of Earth and the other on the surface of the Moon. Both have an initial velocity of 20 m/s. Both objects will take the same time to reach the highest point of their trajectory.

Accepted Answer

The time to reach the highest point depends on the gravitational acceleration, which is different on Earth and the Moon. The Moon's gravity is weaker, so the object there will take longer to reach the highest point.

Question 4

For general projectile motion, the vertical component of a projectile's acceleration

Accepted Answer

In general projectile motion, the only force acting on the projectile in the vertical direction is gravity, which provides a constant acceleration downwards.

Question 5

For general projectile motion, the horizontal component of a projectile's acceleration

Accepted Answer

The horizontal component of a projectile's acceleration is always zero because there is no force acting horizontally on the projectile (assuming there is no air resistance). The projectile moves with constant horizontal velocity, which means there is no change in acceleration in the x-direction. The only force acting on the projectile is gravity, which causes acceleration in the y-direction.

Question 6

If the acceleration vector of an object is directed parallel to the velocity vector,

Accepted Answer

When the acceleration vector is parallel to the velocity vector, it means that the object is accelerating in the same direction as its velocity, causing it to speed up.

Question 7

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.

Accepted Answer

The time it takes to reach the lake depends only on the vertical component of the initial velocity (since there is no air resistance). Both James and John have the same initial vertical velocity (zero), so they will both take the same amount of time to reach the surface of the lake. John's initial horizontal velocity has no effect on the time it takes for him to reach the surface of the lake.

Question 8

If the acceleration vector of an object is directed perpendicular to the velocity vector,

Accepted Answer

When the acceleration vector is directed perpendicular to the velocity vector, it means that the direction of acceleration is changing, resulting in a change of direction of velocity. This is the characteristic of circular motion, where the object moves along a curved path at a constant speed. Therefore, the correct answer is A) the object is turning.

Question 9

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. When they reach the lake below,

Accepted Answer

John has an initial horizontal velocity, so his splashdown speed will be larger due to the combination of his horizontal and vertical velocities. James only has vertical velocity.

Question 10

For a projectile launched horizontally, the horizontal component of a projectile's velocity

Accepted Answer

The horizontal component of a projectile's velocity remains constant throughout its motion because there is no acceleration in the horizontal direction. The only acceleration acting on the projectile is due to gravity, which only affects the vertical component of its velocity.

Question 11

The vertical component of the acceleration of a projectile remains constant during the entire trajectory of the projectile.

Accepted Answer

This is because the vertical acceleration is due solely to gravity, which is a constant acceleration of 9.8 m/s^2 downwards (assuming negligible air resistance). Therefore, the vertical component of acceleration remains constant throughout the projectile's trajectory.

Question 12

The horizontal component of the velocity of a projectile remains constant during the entire trajectory of the projectile.

Accepted Answer

This statement is true. The horizontal velocity of a projectile is constant because there are no horizontal forces acting on the object (assuming air resistance can be neglected). This means that the object is moving at a constant speed in the horizontal direction. The vertical component of the velocity, however, is affected by gravity and changes throughout the trajectory.

Question 13

A ball rolls off the edge of a table. The horizontal component of the ball's velocity remains constant during its entire trajectory because

Accepted Answer

The horizontal component of the ball's velocity remains constant because there is no force acting in the horizontal direction to change it.

Question 14

Two similar objects are thrown simultaneously from the top of a building with the same speed. One is thrown vertically downward, and the other at an angle. Both objects reach the ground at the same time.

Accepted Answer

The object thrown vertically downward will reach the ground first because it travels a shorter path compared to the object thrown at an angle, which has both horizontal and vertical components of motion.

Question 15

A mountain climber encounters a crevasse in an ice field. The opposite side of the crevasse is a height h lower, and is separated horizontally by a distance w. To cross the crevasse, the climber gets a running start and jumps in the horizontal direction. If the height of the crevasse increases but the width remains the same, then,

Accepted Answer

The answer of A mountain climber encounters a crevasse in...

Question 16

For a projectile launched horizontally, the vertical component of a projectile's velocity

Accepted Answer

The vertical component of a projectile's velocity continuously increases due to the acceleration caused by gravity acting downwards.

Question 17

If the acceleration vector of an object is directed anti-parallel to the velocity vector,

Accepted Answer

When the acceleration vector is directed anti-parallel to the velocity vector, it means that the acceleration is in the opposite direction to the velocity. This would cause the object to slow down, as the acceleration is acting against the motion of the object.

Question 18

A pilot drops a bomb from a plane flying horizontally at a constant speed. Neglecting air resistance, when the bomb hits the ground the horizontal location of the plane will

Accepted Answer

The plane will continue to move forward at a constant speed while the bomb falls vertically downwards. Therefore, when the bomb hits the ground, the plane will still be directly above the point where the bomb was released.

Question 19

For general projectile motion, the horizontal component of a projectile's velocity

Accepted Answer

The horizontal component of a projectile's velocity remains a non-zero constant because there is no horizontal force acting on the projectile, so its velocity remains constant unless acted upon by an external force.

Question 20

A rock is thrown at some angle above the horizontal with a certain velocity. It reaches its highest point and starts falling down. What is the velocity of the rock at the highest point of its trajectory?

Accepted Answer

At the highest point of its trajectory, the vertical component of the rock's velocity is 0, but the horizontal component remains unchanged. Therefore, the velocity at the highest point is equal to the initial horizontal velocity.

Quiz 4: Two-Dimensional Kinematics