Newton's Laws of Motion and Momentum

Question 1

State the four features of the forces in a Newton’s third law pair:

Answer 1

-> Same magnitude
-> Same type
-> Acting in opposite directions (along same line)
-> Acting on different objects

Question 2

Explain how crumple zones, seat belts and air bags improve car safety:

Answer 2

During a collision they increase the time taken for the same change in momentum and therefore decrease the the force since force is equal to the rate of change of momentum.

Question 3

State Newton’s First Law

Answer 3

The velocity of an object will not change unless it is acted upon by a resultant force.

Question 4

State the relationship between impulse and momentum:

Answer 4

The impulse of a force is equal to the change in momentum

Question 5

State the principle of conservation of momentum:

Answer 5

The total momentum of a system of objects remains constant, as long as no net external force acts on the system.

Question 6

State the equation given by the conservation of momentum of two objects colliding but not sticking together:

Answer 6

m1u1 + m2u2= m1v1 + m2v2

Question 7

State the equation given by the conservation of momentum for an object that explodes into two pieces:

Answer 7

mu = m1v1 + m2v2
(where m = m1 + m2)

Question 8

State Newton’s Third Law

Answer 8

If object A exerts a force on object B, then B will exert a force back on A of the same size, same type, in opposite directions along the same line.

Question 9

Give the quantities and their units for the equation p = mv

Answer 9

p = momentum (kgms^-1)
m = kg
v = ms^-1

Question 10

State Newton’s 2nd Law

Answer 10

The net force on an object is directly proportional to the object’s rate of change of momentum.

Question 11

Why is momentum still conserved when an object accelerates in free fall?

Answer 11

It is not a closed system - an external force acts (momentum is conserved in the object-Earth system)

Question 12

Give the quantities and their units for the equation F🔼t= 🔼p

Answer 12

F▲t = Impulse (Ns)
▲p = Change in momentum

Question 13

Define Linear Momentum

Answer 13

Linear momentum is the product of mass and velocity (p=mv)

Question 14

State the equation given by the conservation of momentum of two objects that collide and stick together:

Answer 14

m1u1 + m2u2 = mv
(where m = m1 + m2)

Question 15

How should you approach two dimensional collision problems?

Answer 15

Consider conservation of momentum separately in horizontal and vertical directions.

Question 16

What happens to the objects in a perfectly inelastic collision?

Answer 16

They stick together

Question 17

Give three car safety features that reduce the force on passenger during a collision

Answer 17

Crumple zones
Seat belts
Air bags

Question 18

What is represented by the area under the line of a force-time graph?

Answer 18

Impulse (=F▲t = ▲p)

Question 19

What is an elastic collision?

Answer 19

A collision in which total kinetic energy of the objects is the same after as before the collision (no dissipation of energy)

Question 20

Give the quantities and their units for the equation F = ▲p/▲t

Answer 20

F = Force (N)
▲p = Change in momentum (kgms^-1)
▲t = Time taken (s)

Question 21

State two quantities that are conserved in all collisions and explosions in closed systems:

Answer 21

-> Total momentum
-> Total energy (NOT kinetic energy)

Question 22

Define the impulse of a force

Answer 22

The impulse of a force is the product of the average force and time and is equal to the change in momentum (Impulse = F▲t = ▲p)