Tid og sted – Level 2 Flashcards

1
Q

Hvad betyder symbolerne:

s, v, a, g

A

s: sted eller position [m]
v: hastighed [m/s]
a: acceleration [m/s²]
g: tyngdeacceleration [m/s²]

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2
Q

Hvad er tyngdeaccelerationen i Danmark

A

g = 9,82 m/s²

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3
Q

Hvad er tyngdeaccelerationen omkring Jordens nord- og sydpol?

A

g ≈ 9,79 m/s²

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4
Q

Hvordan skrives bremseformlen?

A

u² = 2 ⋅ s ⋅ a + v²

Huske regel: USAv.
u: slutfart, s: bremselængde, a: acc.; v: startfart.

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5
Q

Hvilket symbol angi’r farten til at starte med i bremseformlen:

u² = 2 ⋅ s ⋅ a + v²

A

v: startfart
u: slutfart
Fart måles i meter per sekund.

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6
Q

Du cykler med 10 m/s og bremser med a = –5 m/s².

Hvad bliver bremselængden?

A

s = 10 m.

u² = 2 ⋅ s ⋅ a + v²  ⇄
s = (u² – v²) / (2 ⋅ a)
s = –10² / (2 ⋅ (–5) ) = 10.
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7
Q

Du cykler med 8,0 m/s og bremser hårdt, så accelerationen er a = –8 m/s².
Hvad bliver bremselængden?

A

s = 4 m.

u² = 2 ⋅ s ⋅ a + v²  ⇄
s = (u² – v²) / (2 ⋅ a)
s = –8² / (2 ⋅ (–8) ) = 4.
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8
Q

En bil kører med v = 30 m/s og bremser med a = –10 m/s² indtil hastigheden er u = 10 m/s.
Hvad bliver bremselængden?

A

s = 40 m.

u² = 2 ⋅ s ⋅ a  +  v²  ⇄
s = ( u²  –  v² ) / ( 2 ⋅ a )
s = ( 10² – 30² ) / ( 2 ⋅ (–10) ) 
s = 40.
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9
Q

En bus kører med v = 20 m/s og bremser med a = –8,0 m/s² indtil hastigheden er u = 9,0 m/s.
Hvad er bremselængden?

A

s = 20 m.

u² = 2 ⋅ s ⋅ a  +  v²  ⇄
s = ( u²  –  v² ) / (2 ⋅ a)
s = ( 9² – 20² ) / (2 ⋅ (–8) ) 
s = 319/ 16 ≈ 20.
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10
Q

En bil kører med 54 km/h da en cyklist pludselig besvimer og falder ud på vejen.

Hvad skal accelerationen mindst være for at bremselængden bli’r under 16 meter?

A

a = –7,0 m/s² (…eller mere)

u² = 2 ⋅ s ⋅ a + v²  ⇄
a = (u² – v²) / (2 ⋅ s)

a = –15² / (2 ⋅ 16)
a ≈ –7,0 m/s².

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11
Q

En lastvogn kører med 72 km/h da en barnevogn pludselig triller ud på vejen.

Hvad skal accelerationen mindst være for at bremselængden er under 40 meter?

A

a = –5,0 m/s² (… eller mere!)

u² = 2 ⋅ s ⋅ a + v²  ⇄
a = (u² – v²) / (2 ⋅ s)

a = –20² / (2 ⋅ 40)

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