Dynamics

Question 1

Define mass

Answer 1

Mass is a property of a body which resist change in motion.

Question 2

Define momentum

Answer 2

Momentum of a body is the product of its mass and velocity of a moving body.

Question 3

Define Newton’s First Law

Answer 3

Newton’s first law of motion states that in the absence of resultant force, a body at rest will remain at rest and a body in motion will continue in motion at constant velocity.

Question 4

Define Newton’s Second Law.

Answer 4

Newton’s Second Law of motion states that the rate of change of momentum of a body is proportional to the resultant force acting on the body, and the momentum change takes place in the direction of resultant force.

Question 5

What is the relationship between impulse and change in momentum?

Answer 5

impulse=change in momentum

Question 5

Define impulse

Answer 5

Impulse of a force is the product of average force and the time during which it acts.

Question 6

What is apparent weight?

Answer 6

Apparent weight is the force exerted on the object by the body that is freely supporting it.

Question 7

What is the apparent weight of a free falling body?

Answer 7

zero

Question 8

Define the Principal of Conservation of Momentum

Answer 8

When bodies in a system interact, the total momentum remains constant provided no resultant external force acting on the system.

Question 9

Define elastic collision

Answer 9

Elastic collision is one in which the total kinetic energy is the same before and after the collision.

Question 10

What happens during a head on elastic collision?

Answer 10

relative speed of approach before collision=relative speed of separation after collision
(use when mass is not given)

Question 11

What are the 3 equations that apply to elastic collision?

Answer 11

• Conservation of momentum
• Conservation of KE
• Relative speed of approach=relative speed of separation

Question 12

Define inelastic collision

Answer 12

Inelastic collision is one of which the total kinetic energy is not the same before and after the collision.

Question 13

Define a completely inelastic collision

Answer 13

It is one in which the bodies move together with the same velocity after collision.

Question 14

What is superelastic collisions?

Answer 14

It is where kinetic energy is gained after the collision.

Question 15

What does it meant by a head on collision?

Answer 15

The velocity vectors of the colliding bodies before and after the collision are along the line joining their centre of mass.

Question 16

What does it mean by the total reaction force of a body?

Answer 16

It is the vector sum of the normal reaction force and frictional force acting on the body.

Question 17

What are the 3 kinds of resistance force?

Answer 17

• static friction
• kinetic friction
• viscous force (of liquid/gas)

Question 18

What are the contact forces?

Answer 18

1. Frictional force
2. Normal contact force
3. Tension/ Compression of string,spring or rod
4. Upthrust (acts at the centre of mass of displaced fluid)
5. Lift
6. Thrust

Question 19

What direction does lift act?

Answer 19

Lift act in the direction perpendicular to the relative flow of surrounding fluid

Question 20

What are the 3 car safety features?

Answer 20

• front and rear crumple zones
• seatbelts
• airbags

Question 21

How does the front and rear crumple zones protect passengers during a car crash?

Answer 21

It will collapse during a collision which allows the change in momentum of passengers to take place over a longer time interval, hence reducing the impact force in passenger.

Question 22

How does airbags protect the driver?

Answer 22

It inflates very quickly during a collision and they provide a softer surface to prevent people from hitting hard objects

Question 23

How does seatbelts protect people during a collision?

Answer 23

1. It prevents the person from being thrown around in the car,possibly through the windscreen or hitting themselves on the steering wheel or other objects.
2. The seatbelt also stretches a little, while restraining the person during a crash. The stretching increases the amount of time it takes the person to stop.