PHSX 114 Questions
At what angle should force be applied to a lever arm to achieve minimum torque? [a] 0° [b] 30° [c] 60° [d] 90°
0° The torque acting on a body would be minimized when the angle between the lever arm and the applied force is 0° because sinθ is a minimum at 0°. The torque on a body is T=rFsinθ.
State how many significant figures should be kept in the final result of the following calculation: ((106.7kg)(98.2m)) / ((46.210s)(1.0s)) [a] 2 [b] 4 [c] 5 [d] 6
2 the product of the multiplication should have only 2 significant figures
There is a vector A, with magnitude 5 units pointing towards west and vector B, with magnitude 3 units, pointing towards south. Using vector addition, calculate the magnitude of the resultant vector. [a] |R|= 2.0 units [b] |R|= 4.0 units [c] |R|= 5.8 units [d] |R|= 8.0 units
C it is not correct to directly apply the scalar addition to vectors. Think about the vector law of addition.
For the graph of velocity versus time of a freely falling object, assuming the upward direction as positive, we find that we obtain a straight line with slope of [a] 0 [b] 9.8 m/s² [c] -9.8 m/s² [d] 4.9 m/s²
C the instantaneous acceleration of an object is the slope of the tangent line at the point on the velocity vs time graph
True or False: for a ball thrown straight up in the air, the magnitude of the average velocity, for any time interval, is always greater than the magnitude of its initial velocity
False
True or False: A person walks 2 blocks east and 5 blocks north. Another person walks 5 blocks north and then 2 blocks east. The displacement of the second person.
False Vector addition is commutative. Displacement is a vector quantity. You can calculate the net displacement in both cases by the vector addition method and also compare them.
True or False: the position vs time graph of an object that is speeding up is a straight line
False the graph will not be a straight line as the velocity is not a constant
True of False: can you use the definition of acceleration to explain the units in which acceleration is measured?
True the relationship is true, making acceleration a rate of a rate. This makes acceleration's denominator a product of time multiplied by time
What will be the change in velocity each second if acceleration is 10 m/s/s? [a] an acceleration of 10 m/s/s means that every second, the velocity increases by 10 m/s [b] an acceleration of 10 m/s/s means that every second, the velocity decreases by 10 m/s [c] an acceleration of 10 m/s/s means that every 10 sec, the velocity increases by 10 m/s [d] an acceleration of 10 m/s/s means that every 10 sec, the velocity decreases by 10 m/s
a
Which of the following systems is in stable equilibrium? 1) a skateboard at rest at the bottom of a U-shaped ramp 2) a ball at rest on the edge of a table 3) a quarter, at rest, balanced on its edge [a] system 1 [b] systems 1 and 2 [c] systems 1 and 3 [d] systems 2 and 3
a
a baseball is thrown straight up. Which statement describes the ball at its highest point? [a] its velocity is 0 [b] its acceleration is 0 [c] its velocity is +9.8 m/s² [d] its acceleration is +9.8 m/s²
a acceleration is constant at -9.8 m/s²
identify some advantages of metric units [a] conversion between units is easier in metric units [b] comparison of physical quantities is easy in metric units [c] metric units are more modern than English units [d] metric units are based on powers of 2
a because all units are based on factors of 10
Which kinematic equation would you use to find the velocity of a skydiver 2.0 s after she jumps from a plane and before she opens her parachute? assume the positive direction is downward [a] v = v₀+at [b] v = v₀-at [c] v² = v₀²+at [d] v² = v₀²-at
a before she opens her parachute, she is in a state of free fall with an initial velocity of zero and acceleration due to gravity
Which of the following provides a correct answer for a problem that can be solved using the kinematic equations? [a] A body starts from rest and acceleration at 4 m/s² for 2s. The body's final velocity is 8 m/s. [b] A body starts from rest and accelerates at 4 m/s². The boy's final velocity is 16 m/s. [c] A body with a mass of 2 kg is acted upon by a force of 4N. The acceleration of the body is 2 m/s². [d] A body with a mass of 2 kg is acted upon by a force of 4 N. The acceleration of the body is 0.5 m/s².
a it is a kinematic problem. The final velocity of the body can be obtained by using the kinematic equations.
which situation correctly describes when the moving man's position was negative but his velocity was positive? [a] man moving towards 0 from left to 0 [b] man moving towards 0 from right of 0 [c] man moving away fro 0 from left of 0 [d] man moving away from 0 from right of 0
a the position to the left of zero is negative and since the man is moving towards 0, his motion is rightward and is positive.
What is a component of a two dimensional vector? [a] a component is a piece of a vector that points in either the x or y direction [b] a component is a piece of a vector that has half of the magnitude of the original vector [c] a component is a piece of a vector that points in the direction opposite to the original vector [d] a component is a piece of a vector that points in the same direction as original vector but with double of its magnitude
a this is the correct definition of a component of the vector
A ball is at rest at the highest point on a hill. Is the ball in equilibrium, and if so, what kind of equilibrium? [a] Yes, the ball is in stable equilibrium [b] Yes, the ball is in unstable equilibrium [c] Yes, the ball is in neutral equilibrium [d] No, the ball is not in equilibrium at all
b
A girl throws a ball horizontally from a roof 10 meters high. If air resistance is negligible, how is the vertical velocity of the ball related to its horizontal velocity? [a] the vertical velocity depends on the horizontal velocity [b] the vertical velocity does not depend on the horizontal velocity [c] the vertical and horizontal velocities are the same
b
a train slows down as it pulls into a station, if the train is moving from your left to your right, what are the directions of the vectors for velocity and acceleration? [a] the velocity points to the left and the acceleration vector also points to the left [b] the velocity vector points to the right and the acceleration vector points to the left [c] the velocity vector points to the left and the acceleration vector points to the right [d] the velocity vector points to the right and the acceleration vector also points to the right
b
identify the four variables found in the kinematic equations [a] displacement, force, mass, time [d] acceleration, displacement, time, velocity [c] final velocity, force, initial velocity, mass [d] acceleration, final velocity, force, initial velocity
b
In the equation T=rFsinθ, what is θ? [a] Angle of rotation, that is, angular displacement [b] Angle between the vector r and the vector F [c] Angle between the vector r and the vector T [d] Angle between the vector F and vector T
b Torque is T=rFsinθ , so the angle θ is the angle between the force and the radial vector
You are throwing a ball straight up in the air. describe the ball's velocity and acceleration at the highest point. [a] at the highest point, velocity and acceleration are zero [b] at the highest point, velocity is nonzero but its acceleration is zero [c] at the highest point, acceleration is nonzero, but its velocity is zero [d] at the highest point, velocity and acceleration are both nonzero
c
whats the first step you should take when solving a motion problem using kinematic equations? [a] evaluate the force [b] evaluate the unknowns [c] identify the known values and the unknown variables [d] identify the direction of acceleration
c
if the graph of distance versus time for an object is a straight line with a positive slope, the acceleration is [a] increasing [b] decreasing [c] 0 [d] constant
c The instantaneous velocity of an object is the slope of the tangent line at the point on the distance vs time graph; the acceleration is the rate of change of velocity. Since the slope is constant, there is no change in velocity and therefore the acceleration is 0.
what are the SI units of acceleration? [a] m²/s [b] cm²/s [c] m/s² [d] cm/s²
c meters per second per second
what is the difference between average acceleration and instantaneous acceleration? [a] avg acceleration is the change in displacement divided by the elapsed time whereas instantaneous acceleration is the acceleration at a given point in time [b] avg acceleration is acceleration at a given point in time whereas instantaneous acceleration is the change in displacement divided by the elapsed time [c] avg acceleration is the change in velocity divided by the elapsed time whereas instantaneous acceleration is the acceleration at a given point in time [d] avg acceleration is acceleration at a given point in time whereas instantaneous acceleration is the change in velocity divided by the elapsed time
c think about what average and instantaneous mean
Suppose you take exactly two steps A and B (that is, two nonzero displacements). Under what circumstances can you end up at your starting point? [a] Step A and B are of the same magnitude and in the same direction [b] Steps A and B are of different magnitudes in the same direction [c] Steps A and B are of different magnitudes in opposite directions [d] Steps A and B are the same magnitude in opposite directions
d
You hold a barbell in a horizontal position. The barbell's center of mass is exactly mid-way between two hands. A friend walks up and attaches a weight on the end near your left hand. How does the torque on the bar exerted by your left hand compare to the torque on the bar from your right hand if the bar remains horizontal and at rest? [a] More information is needed to answer [b] The torque from the left hand is less than the torque from the right hand [c] The torque from the left hand is equal to the right hand [d] The torque from the left hand is greater than the torque from the right hand
d
a 0.500 kg hammer, a 6.4 kg bowling ball, a baseball and a tennis ball are all released from rest at the same time from the top of a 50 m cliff. Assuming there is a negligible amount of drag force, which arrives at the ground first? [tip: when a physics problem says a 'negligible' amount, it means the amount is so small that it doesn't affect the experiment enough to matter.] [a] the 0.500 kg hammer [b] the bowling ball [c] the baseball [d] they all hit the ground at the same time
d
if a logarithmic scale is used on a graph, what can you assume about the range of the data? [a] the data consist of numbers that are in decimal form [b] the data consist of numbers in fractional form [c] the data consist of values in exponential form [d] the data extend over a wide range of values
d
When a baseball is thrown straight up, the upward acceleration at the maximum height is [a] 0 [b] increasing [c] decreasing [d] -g
d the acceleration of an object in free fall is never 0, it is a constant 9.8 m/s², downward
Celia and Jane are on the roof of their school. Each woman has an identical ball that they release from the roof at the same time. However, while Celia drops her ball from rest, Jane releases her ball with a small horizontal velocity. Assuming that air resistance is negligible, which ball will hit the ground first? [a] celia's ball [b] jane's ball [c] not enough information [d] the two balls hit the ground at the same time
d vertical velocities are the same, and independent of horizontal velocity