Week 5

Question 1

What is momentum?

Answer 1

The quantity of motion an object possesses

Question 2

Calculation of Linear Momentum (p)

Answer 2

Linear momentum (p) = mass (m) x velocity (v)

p=m*v

Question 3

Which player has greater momentum?

Player 1
m = 110kg
v = 6m/s

Player 2
m = 60kg
v = 8m/s

Answer 3

Player 1 = 660 kg.m/s

Player 2 = 480 kg.m/s

660-480 = 180 kg.m/s of momentum will be exerted towards player 2

Momentum is not lost. Law of Conservation of Momentum.

Question 4

Define conservation of linear momentum

Answer 4

Any given body will continue to move with constant linear
(translatory motion) momentum unless an external force
(linear) acts on the body to change the momentum

Question 5

What is a system in reference to biomechanics?

Answer 5

A system is a sequence of events that you are trying to measure.

e.g. A soccer player kicking a soccer ball is a system. The player, plus the ball before and after impact are required to calculate momentum, conservation of momentum and so on.

Question 6

How to calculate the momentum of a ball after its kicked.

Answer 6

We need to know the mass of both the ball and the player as how fast the system (ball and player running) is going before it’s kicked. And either the ball or the players velocity after the kick.

(mv) ball before + (mv) player before = (mv) ball after + (mv) player after

Question 7

Define impulse

Answer 7

To change the momentum of a system - apply an impulse

Impulse is a force applied over a period of time

Question 8

Equation for impulse

Answer 8

Force x Time

Question 9

What is impulse measured in

Answer 9

Newton seconds

force/time

Question 10

What is the impulse exerted on the water by a rowing oar if an average force for 400 N acts for 0.5s?

Answer 10

400N x 0.5s

200N/s

Question 11

How do you increase impulse?

Answer 11

Greater force over a constrained time period or more time in motion

Question 12

Constant impulse

Answer 12

The greater time over which you absorb the impulse the less the force

Question 13

Define elasticity

Answer 13

the ability of a body or object to return to its original

shape after it has been deformed

Question 14

What is something with high elasticity

Answer 14

Returns to its original shape quickly and the velocity before the collision is very similar as the velocity after the collision.

e.g. golf ball

Question 15

Coefficient of restitution (e)

Answer 15

This measures how much of the kinetic energy before the impact remains as kinetic energy after the impact

Question 16

Coefficient of restitution equation

Answer 16

-e= v after impact / v before impact

e = The square root of - height of ball bounced / height of ball dropped

Question 17

If the coefficient of restitution of an object is 0.15, what would we categorise this ball as?

Answer 17

Inelastic. The higher the number between 0-1, the more elastic the object is.

Question 18

What increases elasticity in a ball?

Answer 18

Increased air pressure and increased temperature

Question 19

What is the coeficient of resistance if a ball is travelling at 15m/s before it hits the ground and -11m/s after

Answer 19

11 / 15 = 0.73

High elasticity