Question 1

For an object moving along a straight line, in order to return to its starting point it does not necessarily have a speed of zero during the time lapse of its motion.

Accepted Answer

The answer of For an object moving along a straight...

Question 2

One centrifuge has twice the diameter of a second one, and half its number of revolutions per minute. Particles in suspension in the two centrifuges will feel the same centripetal acceleration.

Accepted Answer

Centripetal acceleration in a centrifuge is given by the formula $a = \omega^2 r$, where $\omega$ is the angular velocity in radians per second and $r$ is the radius. If one centrifuge has twice the diameter (and thus twice the radius) but half the number of revolutions per minute (which means half the angular velocity), the centripetal acceleration will not be the same because the decrease in angular velocity ($\omega$) is not enough to offset the increase in radius ($r$) when squared in the formula.

Question 3

The figure below shows the velocity of an object as a function of time.
(a) What is the average velocity from the start to the end at 10 s?
(b) What is the displacement of an object from 2 s to 8 s?

Accepted Answer

The answer of The figure below shows the velocity of...

Question 4

If a car brakes at constant deceleration, the stopping distance is doubled when the initial speed is twice as great.

Accepted Answer

The stopping distance increases by a factor of four, not two, when the initial speed is doubled, because stopping distance is proportional to the square of the initial speed when deceleration is constant.

Question 5

A weight is swung on the end of a string in a horizontal plane, with a certain period of revolution. If the string is shortened to half its length, and the revolution period is kept the same, the centripetal acceleration of the weight is halved.

Accepted Answer

The centripetal acceleration is given by a = v^2/r. If the period of revolution is kept the same, then the speed of the weight is also the same. If the string is shortened to half its length, then the radius of the circle is also halved. Therefore, the centripetal acceleration is doubled.

Question 6

Meissner's corpuscles, the mechanism for physiological detection of velocity in humans, detect how fast the body is moving with respect to its surroundings.

Accepted Answer

Meissner's corpuscles are specialized nerve endings in the skin that are responsible for sensitivity to light touch, not for detecting the velocity of body movement with respect to its surroundings.

Question 7

A student drew the coordinate system below to plot major points of interest on the university campus.  (a) What are the coordinates of the classroom, the student centre, and the bus stop in this system?
(b) If the student set up a coordinate system with the origin in the classroom, what would then be the coordinates of the student centre and the bus stop?
(c) How would the distance between the student centre and the bus stop change with the change of a coordinate system?

Accepted Answer

The answer of A student drew the coordinate system below...

Question 8

One athlete can accelerate to a maximum speed of 15 m/s in 2 s, but can maintain that speed for only 20 s. A second athlete reaches a maximum speed of 20 m/s in 2 s, but can maintain it for only 15 s. Which athlete runs the longer distance? Describe your reasoning.

Accepted Answer

The answer of One athlete can accelerate to a maximum...

Question 9

Neglecting air resistance, a ball thrown horizontally with a certain velocity from 10 floors up a building will hit the ground at twice the distance from the building as if it were thrown from 5 floors up.

Accepted Answer

Neglecting air resistance, the horizontal distance a projectile travels is determined by its initial horizontal velocity and the time it is in the air. The time in the air is determined by the vertical component, which depends on the height from which it is dropped. Doubling the height does not double the time in the air since the time to fall is proportional to the square root of the height (from the equation $t = \sqrt{\frac{2h}{g}}$), so the ball thrown from 10 floors up will not hit the ground at twice the distance from the building as if it were thrown from 5 floors up.

Question 10

For a car braking with constant deceleration, the time to stop is doubled when the speed of the car before braking is doubled.

Accepted Answer

The stopping time is directly proportional to the initial speed when deceleration is constant. Doubling the initial speed doubles the stopping time.

Question 11

A ball thrown upward at a given speed will reach the ground with the same speed as the initial speed, regardless of the angle at which it is thrown.

Accepted Answer

Neglecting air resistance, the principle of conservation of energy ensures that a ball thrown upward will return to the ground with the same speed it had when it was launched, regardless of the angle of launch. This is because the kinetic energy lost on the way up is converted into potential energy at the peak of its trajectory, which is then fully converted back into kinetic energy as it falls back to the ground.

Question 12

The figure below shows the x-position of an object as a function of time.
(a) At which point does the object have the smallest non-zero speed?
(b) At which point does the object have the largest speed?
(c) At which point is the object at rest?
(d) At which point is the object moving to the left?

Accepted Answer

The answer of The figure below shows the x-position of...

Question 13

A fly crawls in a zigzag pattern along a line where the angle that successive straight-line segments of its path make with the general direction of motion is 60 degrees. The total distance the fly crawls is twice the distance between the end points of its path.

Accepted Answer

The zigzag pattern described forms an equilateral triangle with each side equal to the distance between the endpoints. Thus, the fly travels two sides of the triangle, which is twice the distance between the endpoints.

Question 14

The mechanism for physiological detection of acceleration of the body in humans is called Meissner's corpuscles.

Accepted Answer

The mechanism for physiological detection of acceleration of the body in humans is primarily through the vestibular system, not Meissner's corpuscles. Meissner's corpuscles are responsible for sensitivity to light touch.

Question 15

Compare the order of magnitude of the accelerations of a human being in a crowd where the average distance apart is 3 m and the speed of walking is 4 km/hr, to those of microscopic particles of the order of 5 ìm apart being jostled by their neighbours several hundreds of times every second.

Accepted Answer

The answer of Compare the order of magnitude of the...

Question 16

One athlete can accelerate to a maximum speed of 15 m/s in 2 s, but can maintain that speed for only 20 s. A second athlete reaches a maximum speed of 20 m/s, but can maintain it for only 15 seconds. Which athlete will have run farther after 10 seconds?

Accepted Answer

The answer of One athlete can accelerate to a maximum...

Question 17

If a car accelerates from a stationary starting position, what difference would it make to the velocity of the car to gradually increase the amount of acceleration to some maximum value, rather than maintain the acceleration at this maximum value from the beginning?

Accepted Answer

The answer of If a car accelerates from a stationary...

Question 18

A bird flies in a straight line at 50 km/hr for 2 minutes, and after taking off again flies in a straight line at 40 km/hr for 3 minutes before landing a second time. What are the maximum and minimum distances that the bird can be from its initial position after the second landing?

Accepted Answer

The answer of A bird flies in a straight line...

Question 19

At some point on the graph of displacement versus time, between two points, the instantaneous velocity equals the average velocity between those points.

Accepted Answer

According to the Mean Value Theorem, for a differentiable function (like displacement vs. time), there exists at least one point where the instantaneous rate of change (instantaneous velocity) equals the average rate of change (average velocity) over an interval.

Question 20

A train travelling at 200 km/hr has to brake due to an obstruction on the track 1 km ahead. The maximum braking deceleration that can be applied is 0.2g. The train will be able to stop before hitting the obstruction.

Accepted Answer

The train's stopping distance can be calculated using the formula: stopping distance = (initial velocity)^2 / (2 * deceleration). Converting 200 km/hr to meters per second gives approximately 55.56 m/s. Using the deceleration of 0.2g (where g = 9.81 m/s²), the stopping distance is (55.56)^2 / (2 * 0.2 * 9.81) ≈ 786 meters, which is less than 1 km (1000 meters), so the train will stop in time.

Quiz 2: Kinematics