mechanics

Question 1

if a ball is 16.8m (at A) from ground what is the displacement when it is 1.2m below A

Answer 1

-1.2

Question 2

if final velocity is 10.5i - 0.9j and initial velocity is 0.6m/s north show that the acceleration is 0.7i-0.1j

find r in terms of t when t is north east

speed t is north east- find t

Answer 2

v=u+at
10.5i-0.9j=0.6j+15a
10.5i-0.9j-0.6j=15a
10.5i-1.5j=15a
a=0.7i-0.1j

from question 2
0.5at@2+ut=r
0.5(0.7i-0.1j)t@2+0.6j(t)=r
0.35it@2-0.05jt@2+0.6jt=r
t(0.35it-0.05jt+0.6j)=r
0.6-0.05t=0.35t
t=1.5

v=u+at
=0.6j+(0.7i-0.1j)t
0.6-0.1t=0.7t
t=0.75

Question 3

find r in terms of t when t is north east

Answer 3

from question 2
0.5at@2+ut=r
0.5(0.7i-0.1j)t@2+0.6j(t)=r
0.35it@2-0.05jt@2+0.6jt=r
t(0.35it-0.05jt+0.6j)=r
0.6-0.05t=0.35t
t=1.5

Question 4

speed t is north east- find t

Answer 4

v=u+at
=0.6j+(0.7i-0.1j)t
0.6-0.1t=0.7t
t=0.75

Question 5

To prove there is a kinematic formula with acceleration given and maybe velocity too

Answer 5

Integrate accelerate
Find the constant c
Integrate velocity
Find constant k

Question 6

What do u do if u calculate time and find that it is negative

Answer 6

Discard it for now try and calculate another quantity

Question 7

When calculating tension of string between car and tow truck

Answer 7

dont include driving force when calcuLating its force

Question 8

When the object sinks what is its final velocity

Answer 8

0 m/s

Question 9

Rules for mechanics when objects are on top of one another…

Answer 9

If p exerts a force on q below find p force
If lift exerts a force on q find q force:
F(ma)= force - 9.8 - p exerting a force on q below
If q exerts a force on p above find the force of p (gravity is greater than tension

Question 10

Prove that a vector passes through origin

Answer 10

Find the points it is in at A and B
If these vector points A and B are parallel then yes it passes through origin

Question 11

To find friction max

Answer 11

First find the thrust
Then find frictional mass (reactive force times coefficient of friction)
If that is greater than thrust use the thrust value to find the friction max

Question 12

When something is about to move up

Answer 12

Draw a diagram including the frictional force going downwards

Question 13

What is a time interval?

Answer 13

Not 1<x<2 but rather 1 second (2-1)

Question 14

Time for one complete revolution

Answer 14

Find consecutive maximum heights

Question 15

For something to be north east of o

Answer 15

I and j should be equal