Chapter 2: Mechanics

Question 1

Displacement

Answer 1

the distance moved in a particular direction (vector)

Question 2

Velocity

Answer 2

how far you have travelled from A to B (vector)

Question 3

Acceleration

Answer 3

the rate of change of velocity (vector)

Question 4

Speed

Answer 4

the rate of change of distance (scalar)

Question 5

Instantaneous velocity

Answer 5

At one particular time

Changes in speed are considerate

Question 6

Average velocity

Answer 6

Over a period of time

distance/(the total time)

Question 7

Identify the acceleration of a body falling in a vaccum near the Earth´s surface with the surface with the acceleration g of free fall

Answer 7

-When we ignore the effect of air resistance on an object falling down to earth due to gravity we say the object is in free fall. Free fall is an example of uniformly accelerated motion as the only force acting on the object is that of gravity.
-On the earth´s surface, the acceleration of an object in free fall is about 9.81 ms-1.
F=ma → F=mg

Question 8

Describe the effects of air resistance on falling objects

Answer 8

• The faster an object’s speed is, the more air resistance it will have. For slow velocities (such as a feather), the air resistance is proportional to the speed, and for fast velocities (such as an airplane), the air resistance is proportional to the square of the speed. For different objects, the exact formula of air resistance is different.
• The net force here is zero, yielding a net acceleration of zero: a constant, terminal velocity is reached.
• Generally heavier objects have faster terminal velocities, since heavy objects require significant magnitude of air resistance (and thus significant velocity) to ballance its significant weight out.

Question 9

Tension

Answer 9

A string that is taut is said to be under tension. Therefore we can say tension (T) is the force that arises in any body when it is stretched. (Note that a string or rope that is not taut has zero tension in it).

Question 10

Up thrust:

Answer 10

An object placed in a fluid medium will experience up thrust. If the up thrust force on a body is equal to the weight, the body will float in the fluid.

Question 11

Hooke’s Law:

Answer 11

Hooke’s law states that up to the elastic limit, the extension, x of a spring is proportional to the tension force, F. The constant of proportionality k is called the spring constant. SI units of spring constant are N m-1.
F∞x
F = Kx

Question 12

Newton’s first law of motion

Answer 12

An object at rest remains at rest, and an object in motion continues in motion with constant velocity (that is, constant speed in a straight line) unless the object experiences a net external force.

Question 13

condition for translational equilibrium

Answer 13

• There is no net force or net torque acting on the body
• No acceleration
  oThe two conditions for transitional equilibrium: the center of mass of the system will not move either left or right, or up or down

Question 14

Newton’s second law of motion

Answer 14

Acceleration is directly proportional to the magnitude of the net force and inversely proportional to the mass if the object.
F=ma

Question 15

linear momentum

Answer 15

the product of mass and velocity

p=mv

Question 16

Impulse

Answer 16

change in momentum over a given period of time

Impulse = F Δt = ΔΡ