1. Tha neach ann an lioft a ghluaiseas suas aig astar cunbhalach. Tha cuideam an neach 800 N. Sa bhad bristear ròpa an lioft, agus mar sin tuitidh an lioft. Obraich a-mach an feachd àbhaisteach air a ghnìomhachadh le làr an lifta don neach dìreach ro agus às dèidh do ròpa an lifta briseadh.
A. 800 N agus 0
B. 800 N agus 800 N
C. 1600 N agus 0
D. 1600 N agus 800 N
Aithnichte:
Weight (w) = 800 Newton
Ag iarraidh: An fheachd àbhaisteach (N)
fuasgladh:
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 luathachadh), so there is no net force to act on the person.
∑F = 0
N – w = 0
N = w
N = 800 Niùton
After the elevator’s rope broke
After the elevator’s rope broke, the elevator and the person saor-thuit together, where the magnitude and the direction of their acceleration same as acceleration due to gravity. There is no normal force on the person.
Is e A am freagairt cheart.
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 feachd frithidh experienced by the block.
A. 0.3 N
B. 1.4 N
C. 2.0 N
D. 3.6 N
Aithnichte:
Tomad (m) = 20 gram
Feachd (F) = 2 Newton
Ag iarraidh: Magnitude of friction force experienced by the block.
fuasgladh:
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 (Fairgead) same as the magnitude of the external force (F)
– The friction force (Fairgead) has opposite direction with the external force (F)
Apply Newton’s first law of motion :
∑F = 0
F – Fairgead = 0
F = Fairgead
Fairgead = 2 Niùton
Is e am freagairt ceart C.
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.
A. 100 N
B. 300 N
C. 600 N
D. 900 N
Aithnichte:
Weight of block (w) = 1350 Newton
hyp = 0.6 m
opp = 0.4 m
A dhìth: The minimum force
fuasgladh:
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).
∑F = 0
F – wx = 0
F = wx
If F = wx, an uair sin object start to moving upward at constant velocity.
wx = w sin θ = (1350)(2/3) = (2)(450) = 900 Newton
Is e D am freagairt cheart.
4. Three forces, F1 = 22 N, F2 = 18 N agus F3 = 40 N act on a block. Which figure describes Newton’s first law.
fuasgladh:
Newton’s first law : Net force (ΣF) = 0.
A. F1 + F.2 - F.3 = 22 N + 18 N – 40 N = 40 N – 40 N = 0
B. F2 + F.3 - F.1 = 18 N + 40 N – 22 N = 58 N – 22 N = 36 N (rightward)
C. F2 + F.3 - F.1 = 18 N + 40 N – 22 N = 58 N – 22 N = 36 N (rightward)
D. F1 + F.3 - F.2 = 22 N + 40 N – 18 N = 62 N – 18 N = 44 N (leftward)
