1. አንድ ሰው ወደ ላይ በሚወጣ ሊፍት ውስጥ ነው የማያቋርጥ ፍጥነት. የ ሚዛን የሰውየው 800 N ነው። የሊፍት ገመዱ ወዲያውኑ ይሰበርና ሊፍት ይወድቃል። መደበኛ ጥንካሬ የአሳንሰሩ ገመድ ከመስበሩ በፊት እና በኋላ በአሳንሰሩ ወለል ላይ ለግለሰቡ ተከናውኗል።
ሀ. 800 N እና 0
ለ. 800 N እና 800 N
ሐ. 1600 N እና 0
መ. 1600 N እና 800 N
የሚታወቅ፦
Weight (w) = 800 Newton
የሚፈለግ መደበኛው ኃይል (ኤን)
መፍትሔው
Before the elevator’s rope broke
When the person stands on the floor of the elevator, weight acts on the person where the direction of the person is downward. That person at rest so that there must a normal force acts on the person, where the direction of the normal force is upward and the magnitude of the normal force same as the magnitude of the weight.
Because the person is at rest in the elevator and the elevator moves at a constant speed (no ፍጥነት), so there is no net force to act on the person.
∑F = 0
N – w = 0
N = w
N = 800 ኒውተን
After the elevator’s rope broke
After the elevator’s rope broke, the elevator and the person በፍጥነት መውደቅ together, where the magnitude and the direction of their acceleration same as acceleration due to gravity. There is no normal force on the person.
ትክክለኛው መልስ ሀ.
2. A block with a mass of 20 gram moves at a constant velocity on a rough horizontal floor at a constant velocity if there is an external force of 2 N acts on the block. Determine the magnitude of the የግጭት ኃይል experienced by the block.
ኤ. 0.3 ኤን
ቢ. 1.4 N
ሲ. 2.0 N
መ. 3.6 N
የሚታወቅ፦
ክብደት (ሜ) = 20 ግራም
ኃይል (ረ) = 2 ኒውተን
የሚፈለግ Magnitude of friction force experienced by the block.
መፍትሔው
Based on Newton’s first law of motion, if a block moves at a constant velocity, then the block has no acceleration. The block moves at a constant velocity, and there is no acceleration if :
– The magnitude of friction force (Fፍሪክ) same as the magnitude of the external force (F)
– The friction force (Fፍሪክ) has opposite direction with the external force (F)
Apply Newton’s first law of motion :
Σረ = 0
ኤፍ - ኤፍፍሪክ = 0
ረ = ረፍሪክ
Fፍሪክ = 2 ኒውተን
ትክክለኛው መልስ ሲ ነው።
3. A smooth inclined plane with the length of 0.6 m and height of 0.4 m. A block with the weight of, 1350 N will move upward using the inclined plane. Determine the magnitude of force need to move the block.
ኤ. 100 ኤን
ቢ. 300 N
ሲ. 600 N
መ. 900 N
የሚታወቅ፦
Weight of block (w) = 1350 Newton
hyp = 0.6 m
opp = 0.4 m
የሚፈለግ፦ The minimum force
መፍትሔው
hyp = ac = 0.6 m
opp = bc = 0.4 m
Sin θ = bc / ac = 0.4 / 0.6 = 4/6 = 2/3
Based on Newton’s first law of motion, the block start to moves upward then the external force (F) minimal same as the horizontal component of weight (wx).
Σረ = 0
ኤፍ - ወx = 0
ረ = ወx
If F = wx, ከዚያ object start to moving upward at constant velocity.
wx = w sin θ = (1350)(2/3) = (2)(450) = 900 Newton
ትክክለኛው መልስ ዲ ነው።
4. Three forces, F1 = 22 N, F2 = 18 N እና F3 = 40 N act on a block. Which figure describes Newton’s first law.
መፍትሔው
Newton’s first law : Net force (ΣF) = 0.
ኤ. ኤፍ1 + ረ2 - ረ3 = 22 N + 18 N – 40 N = 40 N – 40 N = 0
ቢ. ኤፍ2 + ረ3 - ረ1 = 18 N + 40 N – 22 N = 58 N – 22 N = 36 N (rightward)
ሲ. ኤፍ2 + ረ3 - ረ1 = 18 N + 40 N – 22 N = 58 N – 22 N = 36 N (rightward)
ዲ. ኤፍ1 + ረ3 - ረ2 = 22 N + 40 N – 18 N = 62 N – 18 N = 44 N (leftward)
