3.5 Newton's laws of motion

Question 1

What is the equation for momentum?

Answer 1

Momentum = mass x velocity

Question 2

What are the units for momentum?

Answer 2

kg m s -1 or N s

Question 3

What sort of quantity is momentum?

Answer 3

Vector quantity

Question 4

What happens to momentum during a collision or interaction?

Answer 4

Momentum is conserved during any collision or interaction-the total momentum before the collision/ interaction/ explosion, is equal to the momentum after, provided no external forces are present.

Question 5

What is momentum directly proportional to?

Answer 5

Momentum is directly proportional to both the mass of a moving object and its velocity- doubling either would mean the momentum would double.

Question 6

What is the principle of conservation of momentum?

Answer 6

The principle of momentum is the total momentum before a collision is always equal to the total momentum after the collision, provided no external forces are involved.

Question 7

How many laws of motion does Newton have?

Answer 7

3

Question 8

What do Newtons laws of motion explain?

Answer 8

How forces cause bodies to remain stationary, move at a constant speed or accelerate.

Question 9

What is Newton’s 1st law?

Answer 9

A body will remain at rest or continue to move at constant velocity until an external force is applied to it.

Question 10

What is Newton’s 2nd Law?

Answer 10

The resultant force on an object is proportional to the rate of change of momentum of the object, and the momentum change takes place in direction of the force.

Question 11

What is Newton’s 3rd law?

Answer 11

If an object exerts a force on object B, then object B will exert an equal and opposite force on object A.
For this to work, there must be two objects and the forces exerted by one object must be the same type.

Question 12

What does a force-time diagram look like? What does the area underneath represent?

Answer 12

Area underneath represents impulse of the force.

Question 13

Define impulse.

Answer 13

Impulse= force x change in time.

Question 14

What are the units for impulse?

Answer 14

N s or kg m s^-1

Question 15

How cam you combine F=ma and a=(v-u)/t

Answer 15

a=(v-u)/t

F/m=(v-u)/t

F=m(v-u)/t

F=(mv-mu)/t

F= change in p/ change in t

Question 16

What is an elastic collision?

Answer 16

A collision where momentum and the kinetic energy are conserved- no energy is transferred to other for,ms such as heat or sound.

Question 17

What is an inelastic collision?

Answer 17

A collision where momentum is conserved but some of the kinetic energy is transferred to other forms in the collision- there is less kinetic energy after the collision compared to before.

Question 18

what sort of collisions occur in nature?

Answer 18

Inelastic collisions- there is no truly elastic collisions in nature- energy is always transferred into other forms.

However, collisions between gas atoms are usually taken to be perfectly elastic.

Question 19

What 3 things are always conserved?

Answer 19

• Energy
• Charge
• Momentum

Question 20

What happens to the momentum in a collision in two dimensions?

Answer 20

For collisions which do not take place in a straight line, we have to ensure that the momentum, in two perpendicular directions is conserved.

Question 21

How can you work out impulse with momentum?

Answer 21

Impulse= change in momentum

Question 22

How is momentum conserved when a grenade explodes?

Answer 22

The grenade will be stationary initially, before the explosion, so the total momentum is zero. This also needs to be true after the explosion as momentum is always conserved. This means that mass will fly off in different directions as different velocities once the grenade explodes. The pieces with positive momentum (mv) will cancel with all of the pieces that have negative momentum (-mv) and the total momentum of the grenade pieces will add up to zero.