Forces 2 (Phy)

Question 1

momentum (+ eq.)

Answer 1

the measure of the tendency of an object to keep moving / how hard it is to stop moving

= mass x velocity
p = mv

Question 2

unit for momentum

Answer 2

kgm/s

Question 3

conservation of momentum

Answer 3

total momentum before a collision = total momentum after a collision
(unless acted on by a external force)

Question 4

impact force =

Answer 4

change in momentum over time
= mv - mu / t

if mass stays same:
m(v-u/t)

Question 5

impact forces: greater mass & same force

Answer 5

increases time

Question 6

stopping distance

Answer 6

how far a car travels before it stops

= thinking distance - breaking distance

Question 7

for a car to stop moving …

Answer 7

kinetic energy has to change into heat energy at the brakes and tyres of the car

Question 8

thinking distance

Answer 8

distance the car travels in a split second between a hazard appearing and driver applying the breaks

Question 9

what affects thinking distance

Answer 9

how fast car is gong
how intoxicated you are
your concentration

Question 10

braking distance

Answer 10

distance car travels during deceleration whilst breaks are being applied

Question 11

what affects breaking distance

Answer 11

speed of car
mass of car
condition of brakes
condition of tyres
condition of road

Question 12

how does thinking distance change with speed

Answer 12

= 3/10 x speed (mph)

Question 13

stopping distance at 20

Answer 13

12

Question 14

stopping distance at 30

Answer 14

23

Question 15

stopping distance at 40

Answer 15

36

Question 16

stopping distance at 50

Answer 16

53

Question 17

stopping distance at 60

Answer 17

73

Question 18

stopping distance at 70

Answer 18

96

Question 19

fluid

Answer 19

a substance that can flow (eg liquid or gas)

Question 20

3 stages of falling

Answer 20

at the start, the object accelerates downwards due to the force of gravity

as the object’s speed increases, frictional forces such as air resistance or drag increase

at terminal velocity, the weight of the object due to gravity is balanced by the frictional forces, and the resultant force is zero

The weight of an object does not change as it falls, as long as it stays whole.

Question 21

object with ____ mass fall faster through a fluid

Answer 21

greater- more weight and same fluid resistance

Question 22

how would i improve my experiment about terminal velocity?

Answer 22

more repeats
do it over a larger distance

Question 23

elastic limit

Answer 23

past it:
- materials no longer show elastic behaviour (do not return to original size when stretching force is removed)
- materials permanently deformed
- material weaker (fracture of some atomic bonds)

Question 24

Hooke’s Law

Answer 24

f = kx
force = spring constant x extension

Question 25

spring constant (k)

Answer 25

stiffness of spring
- units of Nm-1
- higher k is, the stiffer the spring
- materials with higher k need a large force for a given extension

Question 26

how to interpret force extension graph

Answer 26

force on y axis, extension on bottom !!
gradient is k

therefore:
steeper line means stiffer (high k)
gentle line means less stiff (low k)

Question 27

why is hookes law important

Answer 27

• for construction of structures (eg bridges buildings)
• for vehicle design (deformation of materials)

Question 28

lever

Answer 28

long bar that pivots
- when you push down on one side (effort), the load (object on the other end) moves up

Question 29

moment (+ units + eq.)

Answer 29

turning force
- Nm
= force x perpendicular distance

Question 30

how to do balanced moments question

Answer 30

F1 / F2 = L2 / L1

Question 31

size and gears

Answer 31

If the driven gear is made larger is will rotate more slowly but with a greater moment. For example, a low gear ratio on a bike or car.
If the driven gear is made smaller it will rotate more quickly but with a smaller moment. For example, a high gear ratio on a bike or car.

Question 32

gears

Answer 32

Gears are wheels with toothed edges that rotate on an axle or shaft. The teeth of one gear fit into the teeth of another gear. This lets one gear turn the other, meaning one axle or shaft can be used to turn another shaft.

The forces acting on the teeth are identical for both gears, but their moments are different

Question 33

centre of mass

Answer 33

the point where the weight of the object acts

Question 34

centre of mass of different shapes

Answer 34

even sided: join up opposite corners
odd sided: join up point to midpoint

Question 35

explosion

Answer 35

when the momentum before the collision is 0, the momentum after will be zero

velocities will be equal and in opposite directions

Question 36

car safety

Answer 36

helmets increase impact time

seat belt increases time to stop - reduces force
seatbelt is on chest so spreads force out, otherwise force would be applied to head

airbag does both these

Question 37

why are soft surfaces good for collisions

Answer 37

cushioning effect- duration of impact is longer