Mechanics Reasoning

Question 1

Explain how …. Modelled as a particle (moments)

Answer 1

Weight acts as/at a point

Question 2

Beam is modelled as a rod

Answer 2

Remains rigid and doesn’t bend

Question 3

Pulleys + connected particles: explain which modelling assumptions you have used

Answer 3

The string is inextensible

Question 4

Explain how you used the fact the pulley is smooth

Answer 4

Tension is the same

Question 6

How you have used the fact the string is light

Answer 6

Tension is the same

Question 7

Cable/string is inextensible

Answer 7

Acceleration is the same

Question 8

What would happen is mew is greater than 1

Answer 8

The particle wouldn’t move

Question 9

Uniform rod

Answer 9

Weight acts at the centre of the body

Question 11

If asked the force on the pulley

Answer 11

Move the forces so they become a triangle
Use cosine rule
If particles and pulley resemble triangle alr /*\ shape make triangle and angles should add up to 90°
Use Pythagoras

Question 12

When overtakes B…

Answer 12

Distances should be the same, find an expression for distance for both particles and solve for time.
This works bc distances travelled the same but one is going faster, e.g if Lec has a faster lap time will overtake someone going slower but distance is the same

Question 13

Lift with stacked load and asked to find the reaction of one load on the another

Answer 13

If on top: reaction acts upwards
If on bottom: reaction acts downward + reaction force upwards from lift!
Use in F=ma with the acceleration given/found
(If on top, the reaction acting upwards is the thing that drives the movement (not the tension) so use lift’s acceleration)