4.1 - 4.9

Question 1

define the Newton

Answer 1

the force required to give a 1-kilogram mass an acceleration of 1 m/s^2

Question 2

what is Newton’s first law

Answer 2

an object will maintain its current velocity unless acted upon by a resultant force

Question 3

what is Newton’s second law

Answer 3

the rate of change of momentum is directly proportional to the resultant force and takes place in the direction of that force

Question 4

what is Newton’s third law

Answer 4

when two objects interact they exert an equal but opposite force on the other

Question 5

define ‘weight’

Answer 5

the gravitational force on an object measured in newtons

Question 6

what is the centre of mass

Answer 6

the point through which any externally applied force produces a straight line motion and no rotation

Question 7

what is the centre of gravity

Answer 7

an imaginary point where all of the weight of an object appears to act

Question 8

how can you find the centre of mass of a 2d object

Answer 8

make a hole in the object and hang it on a pin. draw a straight line down using a plumb-line hung from the pin and then do the same thing after rotating the object. where these two lines intersect is the position of the centre of mass

Question 9

how is a free-body diagram drawn

Answer 9

each force is represented by a labelled arrow pointing in the direction the force acts. each arrow is drawn to scale (longer arrow’s show a greater force)

Question 10

define ‘terminal velocity’

Answer 10

the constant speed reached by a falling object when the drag force is equal but opposite to the weight

Question 11

factors affecting drag

Answer 11

speed,
cross-sectional area,
density of fluid

Question 12

relationship between drag and speed

Answer 12

drag is directly proportional to the speed squared

Question 13

define the moment of a force

Answer 13

the product of force and the perpendicular distance between the line of action of the force and the point of rotation

Question 14

what is the principle of moments

Answer 14

for an object in rotational equilibrium the sum of the clockwise moments equals the sum of the anticlockwise moments about a point

Question 15

define a ‘couple’

Answer 15

a pair of equal and opposite coplanar forces acting on an object but not in the same straight line

Question 16

what is the torque of a couple

Answer 16

the product of one of the forces of the couple and the perpendicular distance between them

Question 17

what does it mean when three forces add to form a triangle

Answer 17

the net force is zero so the object they are acting on is in equilibrium

Question 18

define density

Answer 18

the mass per unit volume of a substance

Question 19

define pressure

Answer 19

the force exerted per unit area. measured in pascals

Question 20

what is Archimedes principle

Answer 20

the upthrust on an object in a fluid is equal to the weight of the fluid displaced

Question 21

how can you find the volume of an irregular solid

Answer 21

partially fill a measuring cylinder with water. place the irregular solid inside it (ensure it’s fully submerged). find the difference between the initial and final volume displayed on the cylinder. that is the volume of the object.

Question 22

what is a fluid

Answer 22

a substance that can flow. it includes gases and liquids

Question 23

how can the equation for the pressure exerted by a fluid be derived

Answer 23

start with Weight = mass of column * g. mass is the densityvolume and volume is the cross-sectional areaheight so W=ρAhg. the pressure this exerts equals the weight/cross-sectional area so
P= W/A= ρAhg/A= ρhg. so Pressure=ρhg

Question 24

how can you derive the equation for the upthrust on a submerged object

Answer 24

start with pressure=ρgh at the top of the object. the pressure at the bottom of the object is (x+h)ρh where x is the object’s height. since P=F/A, F=PA. therefore the resultant upthrust on the object is
(h+x)ρgA - hρgA= xρgA.