Tukaj so zbrane vaje in rešitve za poglavje Sile pri fiziki v 8. razredu: Spletna gradiva z vajami in rešitvami Interaktivne vaje : Na portalu Interaktivne-vaje.si najdete naloge o merjenju sil, masi in teži ter Hookovem zakonu s takojšnjo povratno informacijo. OpenProf : Celovita zbirka nalog, ki pokriva seštevanje sil, Newtonove zakone, gravitacijo ter trenje in upor, je na voljo na OpenProf.com . iUčbeniki : Interaktivno snov s simulacijami in nalogami lahko predelate v e-učbeniku za fiziko 8 . Arnes Učilnice : Različni učitelji objavljajo delovne liste in vaje, kot so te na OŠ Vrhovci , ki vključujejo tudi rešitve za opis in risanje sil. Ključne teme za utrjevanje Opis in risanje sil : Razumevanje sile kot vektorske količine (prijemališče, smer, velikost) in risanje v merilu (npr. ). Masa in teža : Izračun teže s formulo (kjer je ); npr. knjiga z maso ima težo . Hookov zakon : Razumevanje, da sta sila in raztezek vzmeti premosorazmerna ( ). Sestavljanje in razstavljanje sil : Iskanje rezultante vzporednih (seštevanje/odštevanje) in nevzporednih sil (paralelogram sil). Trenje in upor : Sile, ki zavirajo gibanje in so odvisne od hrapavosti ploskev (trenje) ali oblike telesa in hitrosti (upor). Primeri rešenih nalog Ravnovesje : Če na sani oče vleče naprej s silo , bratec pa nazaj s , je rezultanta v smeri očeta. Hookov zakon : Če sila raztegne vzmet za , bo sila to isto vzmet raztegnila za . Za dostop do celotnih rešitev samostojnega delovnega zvezka (SDZ) založbe Mladinska knjiga lahko obiščete FlipHTML5 . Ali te zanima specifičen izračun (npr. rezultanta sil ali Hookov zakon) ali iščeš celoten delovni list za tisk? fizika-8.-a-8.-b-rešitve-sile.pdf
1. Key Theory Recap (Before Solving) Force (sila) – something that changes the state of motion or shape of a body. Unit: newton (N) Tool: spring scale (vzmetno tehtnico) Main types of forces in 8th grade:
Gravitational force (teža) – ( F_g = m \cdot g ) ( g \approx 10 , \text{N/kg} ) (on Earth) Spring force (prožnostna sila) – ( F_{pr} = k \cdot \Delta l ) (Hooke’s law) Friction (trenje) – static and kinetic Buoyancy (vzgon) – ( F_{vz} = \rho_{tekočine} \cdot g \cdot V_{potopljenega} ) Resultant force (rezultanta) – sum of forces in same/opposite direction.
2. Typical Exercises with Step-by-Step Solutions Exercise 1: Weight (Teža) Question: Calculate the weight of a 4 kg iron ball. ((g = 10 , \text{N/kg})) Solution: [ F_g = m \cdot g = 4 \cdot 10 = 40 , \text{N} ] Answer: 40 N fizika 8 razred vaje in resitve sile
Exercise 2: Spring force (Hooke’s law) Question: A spring extends by 3 cm when a 6 N force is applied. What is the spring constant (k)? How much will it extend under 10 N? Solution:
(F = k \cdot \Delta l \Rightarrow k = \frac{F}{\Delta l} = \frac{6}{0.03} = 200 , \text{N/m}) (\Delta l = \frac{F}{k} = \frac{10}{200} = 0.05 , \text{m} = 5 , \text{cm})
Answer: (k = 200 , \text{N/m}), extension = 5 cm Tukaj so zbrane vaje in rešitve za poglavje
Exercise 3: Friction force Question: A 50 N box is pulled horizontally at constant speed. Friction coefficient (\mu = 0.4). What is the pulling force? Solution: At constant speed: (F_{pull} = F_{tr}) [ F_{tr} = \mu \cdot F_g = 0.4 \cdot 50 = 20 , \text{N} ] Answer: 20 N
Exercise 4: Buoyancy Question: A wooden cube (side 10 cm) floats in water. Density of wood 600 kg/m³, water 1000 kg/m³. What volume is submerged? Solution: Equilibrium: (F_{vz} = F_g) [ \rho_{water} \cdot g \cdot V_{sub} = \rho_{wood} \cdot g \cdot V_{total} ] [ V_{sub} = \frac{\rho_{wood}}{\rho_{water}} \cdot V_{total} ] [ V_{total} = (0.1)^3 = 0.001 , \text{m}^3 ] [ V_{sub} = \frac{600}{1000} \cdot 0.001 = 0.0006 , \text{m}^3 = 600 , \text{cm}^3 ] Answer: 600 cm³ (60% submerged)
Exercise 5: Resultant force Question: Two forces act on a body: 15 N right, 10 N left. Find resultant. Solution: [ F_{rez} = 15 - 10 = 5 , \text{N} \ (\text{to the right}) ] Answer: 5 N right iUčbeniki : Interaktivno snov s simulacijami in nalogami
Exercise 6: Motion and force relationship Question: A 2 kg object accelerates at (3 , \text{m/s}^2). What net force acts on it? Solution: [ F = m \cdot a = 2 \cdot 3 = 6 , \text{N} ] Answer: 6 N
3. Mixed Practice Problems (with answers) | Problem | Answer | |---------|--------| | 1. Weight of 500 g mass ((g=9.8)) | 4.9 N | | 2. Spring (k=250 , \text{N/m}), force 20 N → extension | 0.08 m (8 cm) | | 3. Mass from weight 120 N | 12 kg | | 4. Force needed to move 200 N box, (\mu=0.2) | 40 N | | 5. Buoyant force on 0.02 m³ object fully in water | 200 N | | 6. Resultant of 8 N N, 5 N S, 3 N N | 6 N North | | 7. Acceleration of 10 kg object under 25 N net force | 2.5 m/s² | | 8. Cube 5 cm side, half submerged in oil ((\rho=800)) → buoyancy | (0.5 \cdot 0.000125 \cdot 800 \cdot 10 = 0.5 , \text{N}) |