moments, levers and gears (topic 5)

Question 1

Answer 1

• weight of beam acts half way along the length of it
• 0.6 m

Question 2

explain what is meant by the principle of moments (1)

Answer 2

• the sum of the clockwise moments is equal to the sum of the anti-clockwise moments for a body to be in equilibrium

Question 3

calculate the value force X must have to keep the beam in equillibrium, clockwise moment is 24 N m

Answer 3

Question 4

the student climbs on the board at the centre and walks towards the right hand end, describe how the clockwise moment due to the weight of the student varies as the student walks along the board (2)

Answer 4

• as the student walks towards the end of the board, the distance between the student and the pivot increases
• the clockwise moment due to the student increases

Question 5

a student of weight 500N stands on the right hand end of the diving board, the student places a mass 50cm from the left hand end of the board to prevent it toppling, calculate the unknown mass required to prevent the board toppling

Answer 5

Question 6

the weight of the beam is 120 N and the weight of the painter is 500 N, in the position shown, the support force at A is 100 N, calculate the support force at B

Answer 6

• total downwards force = 500 + 120 = 620 N
• total downwards force = A + B
• B = total downwards force - A
• B = 620 - 100 = 520 N

Question 7

describe how the support forces vary as the painter walks to the left (1)

Answer 7

as the painter walks to the left, support force B decreases and support force A increases

Question 8

the painter is now 1 m from B. The total length of the beam is 2.5 m, calculate the support forces A and B

Answer 8

Question 9

name the point labelled X

Answer 9

centre of mass

Question 10

calculate the clockwise moment due to the weight of the card, 0.02 N

Answer 10

Question 11

calculate the horizontal force the student needs to apply to keep the card in equilibrium, clockwise moment = 0.0001Nm

Answer 11

Question 12

calculate the resultant moment for the students on the see-saw

Answer 12

Question 13

calculate the distance from X that student B should sit for the see-saw to be in equilibrium

Answer 13

Question 14

Answer 14

Question 15

describe what happens to the reading on the newton-metre as the 200 g mass is moved to the left (3)

Answer 15

• as the 200 g mass is moved to the left, the clockwise moment reduces
• anticlockwise moment reduces by same amount
• reading on newton-metre reduces

Question 16

calculate the upwards force that Joe needs to apply to keep the suitcase in equilibrium, weight of the case is 254.8 N

Answer 16

Question 17

Joe says increasing the length of the handle would makes it easier to keep the suitcase in equilibrium, assume the distance between the centre of mass and the pivot remains the same, explain if Joe is correct (3)

Answer 17

• correct
• clockwise moment is still the same
• the distance between the handle and the pivot has increased
• therefore a lower force is required to give the same moment

Question 18

when there was no mass added to the metre ruler, there was still a reading of 0.05N on the newton-metre, explain why (2)

Answer 18

• the mass of the ruler is causing a clockwise moment about the pivot
• the newton-metre must provide the anticlockwise moment to keep the ruler in equilibrium

Question 19

calculate the weight of the ruler

Answer 19