Define work done by a constant force
Scenario
Aap subah se ek heavy deewar ko dhakka maar rahe ho, paseena chhoot gaya, par deewar apni jagah se hil nahi rahi.
Kya physics ke hisaab se aapne sach mein koi kaam (work) kiya hai?
Mental model
Work tabhi hota hai jab force lagane par object apni jagah se actually move kare.
Agar aap force lagate hain par koi displacement nahi hoti, toh physics mein work done zero hota hai. Work depends on both effort (force) and result (displacement).
Explanation
Everyday language mein 'work' ka matlab koi bhi physical ya mental effort hota hai. Par physics mein, work is defined very strictly. Work is said to be done ONLY when a force acts on an object, and the object is displaced in the direction of the force.
Mathematically, jab ek constant force `F` lagta hai ek object par, aur object usi direction mein distance `s` move karta hai, toh work done `W` ko define karte hain as the product of force and displacement. Yaani: `W = F × s`.
Work ek scalar quantity hai, iska matlab ismein sirf magnitude hota hai, direction nahi. Aise mat sochna ki force aur displacement vectors hain toh work bhi vector hoga.
Work ka SI unit Joule (J) hota hai, named after James Prescott Joule. Ek Joule ka work tab hota hai jab 1 Newton ka force kisi object ko 1 meter tak displace karta hai usi force ki direction mein. `1 J = 1 N × 1 m`.
Worked example
Problem: A force of 5 N is acting on an object. The object is displaced through 2 m in the direction of the force. If the force acts on the object all through the displacement, what is the work done?
- Pehle check karo ki force aur displacement kitna diya hai.
- Kyunki force aur displacement same direction mein hain, hum direct formula lagayenge.
- Values put karke calculate kar lo.
Answer: 10 J
Problem: A person pushes a trolley with a force of 50 N, and the trolley moves a distance of 4 m in the same direction. Calculate the work done by the person.
- Force aur displacement same direction mein diye hain.
- Work ka simple formula use karenge.
- Multiply the values.
Answer: 200 J
Key points
- Formula for Work: W = F s, where F is force and s is displacement.
- SI Unit: The SI unit of work is Joule (J). 1 J = 1 N m.
- Conditions for Work: A force must be applied, and there must be displacement.
Common mistakes
- Confusing mental effort with physical work: Exam ke liye padhai karte time aap thak jaate ho, par physics ke hisaab se agar aap apni jagah par baithe ho, toh work done is zero. Displacement hona zaroori hai.
- Forgetting the unit: Work hamesha Joules (J) mein measure hota hai. Sirf number mat likhna, J zaroor lagana, warna marks kat jayenge.
Recall questions
- What is the formula for work done by a constant force?
- What is the SI unit of work?
- What two conditions are required for work to be done?
- Is work a scalar or vector quantity?
Questions & answers
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force. Let us take it that the force acts on the object through the displacement. What is the work done in this case?
56 J
Approach: Multiply force (7 N) by displacement (8 m).
Define 1 Joule of work.
1 Joule is the amount of work done when a force of 1 Newton displaces an object by 1 meter along the line of action of the force.
Approach: Use the formula W = Fs, set F = 1 N and s = 1 m.
Continue learning
Next: Identify zero work conditions
Next: Interpret negative work