Mechanics

Question 1

a vector quantity has both…

Answer 1

Direction and magnitude (oh yeah)

Question 2

If I drive 15 km to Pak’n’save (detouring to recoil at New World prices), and Pak’n’save is 10 km away from where I started, which of these quantities is distance and which is displacement?

Answer 2

The distance is 15 km, and the displacement is 10 km.

Question 3

At the top of the path of a projectile, vertical velocity is…

Answer 3

0 m/s

Question 4

How would you add two vectors that are neither parallel or perpendicular to each other (i.e. are weird)

Answer 4

Resolve both into x and y components, then add.

Question 5

What is Newton’s third law?

Answer 5

Every action has an equal and opposite reaction.

Question 6

What is Newton’s first law?

Answer 6

The law of inertia (the movement of an object will not change unless acted upon

Question 7

What is Hooke’s law?

Answer 7

F = k x
F= force on spring
k= spring constant
x= extension/compression from equilibrium

Question 8

Every spring has an elastic limit. What happens to a spring past it’s elastic limit?

Answer 8

The spring deforms, and Hooke’s law no longer holds (f and x no longer increase proportionally)

Question 9

What is torque?

Answer 9

Force applied at a distance

Question 10

If an object is not moving / at an equilibrium, what two quantities are balanced?

Answer 10

Clockwise torque = Anticlockwise torque
Up force = down force

Question 11

When working with an object that is fixed at two sides (say, a bridge), choose where as a pivot point?

Answer 11

a pier as a pivot point (it is arbitrary, but easy to work with)

Question 12

What is frequency?

Answer 12

Oscillations per second ( n/t )

Question 13

What is period?

Answer 13

Seconds per oscillation ( t/n )

Question 14

How do you calculate circular speed?

Answer 14

v= d/t, since d= circumference, d= 2(pi)r, velocity is v = 2(pi)r/t

Question 15

How do you calculate centripetal acceleration (the acceleration curving the path of the object closer to the centre)?

Answer 15

a=v squared/r

Question 16

How do you calculate centripetal force?

Answer 16

As f=m x a, centripetal force is f = (m x v squared) / r

Question 17

In the “Jelly spinning on the plate” example, why does the jelly stay on the plate?

Answer 17

The friction between the jelly and the plate provides centripetal force that negates the effect of inertia.

Question 18

What is momentum?

Answer 18

Mass in motion

Question 19

What is impulse?

Answer 19

Change in momentum

Question 20

If I dropped a coin from my roof, and I threw a coin straight upwards, what would be the downwards acceleration for both objects?

Answer 20

They would both be 9.8 m/s squared.

Question 21

If you do not consider friction, energy is…

Answer 21

conserved (not destroyed, only converted to a different form.

Question 22

What is the equation for momentum?

Answer 22

p=mv

Question 23

What is the equation for impulse?

Answer 23

▲p= ft

Question 24

There are two rotisserie chickens. One is dropped on a pillow, and another is dropped on a concrete slab. How can the equation for impulse help explain the state of the chickens after the drop?

Answer 24

When the chickens slow down, they must lose their momentum (p=mv, v is 0), so they each must experience an impulse (▲p). Impulse is force exerted over time (▲p=ft), and it is force that causes the chicken to turn into a Jackson Pollock painting. The pillow can deform, so it allows for more time for the chicken to decellerate (larger t means less f), and the chicken is relatively intact. The concrete cannot deform, so it has a very small t number, so it must have a large force to exert the proper impulse, splatting the chicken.

Question 25

Because energy is conserved (and friction is not considered in exam papers), what equations can be seen as equivalent?

Answer 25

1/2 m v squared = m g h (or 1/2 k x squared if you’re a spring)
▲Ek = ▲Ep

Question 26

If you kick a ball on a curve-like path, not considering friction, what values can be considered constant?

Answer 26

Vertical acceleration and horizontal speed

Question 27

What is the difference between an elastic and an inelastic collision?

Answer 27

Kinetic energy does not change in an elastic collision, energy is converted into different forms in an inelastic collision.

Question 28

What is conserved in both elastic and inelastic collisions?

Answer 28

Momentum (only if you consider the collision a whole system)