starter

• My mass is about 75 kg. When I climb my stairs, I rise vertically by 3 metres. – What is my weight (in newtons)?

750 N• How much gravitational potential energy do I

gain?2250 J

MomentumL.O.

Calculate the momentum of a moving object.

To use the conservation of momentum to calculate the mass, velocity or momentum of a body involved in a collision or explosion.

Homework: Kinetic Energy and Basic Momentum Calculations worksheet

How will the truck and car move after they crash into each other?

The momentum of an object = its mass x its velocity

Use a calculator to work out the momentum in each of these cases:

• Jack has a mass of 50 kg and runs with velocity 8 m/s.

• A truck of mass 40 000 kg is travelling at 18 m/s (40 mph).

• A car of mass 1000 kg is travelling at 31.6 m/s (70 mph).

• A train with a mass of 120 000 kg has a velocity of 40 m/s (about 90 mph).

• The Earth has a mass of 6 1024 kg and is moving around the Sun with a velocity of 30 000 m/s (about 67 000 mph). Calculate the Earth’s momentum.

• A crash report says ‘The train had a momentum of 3 790 000 kg m/s.’ If the train had a mass of 120 000 kg, what was its velocity?

Investigating collisions.

Work out the momentum of the objects before and after the collision. Remember momentum have a direction as well as size.

Momentum is conserved whenever objects interact, provided no external forces act on them.

To do:

Workbook page 70

MomentumL.O.

Calculate the momentum of a moving object.

To use the conservation of momentum to calculate the mass, velocity or momentum of a body involved in a collision or explosion.

Marking Homework

• 1a) KE = ½mv2 = ½ x (400) x (15)2

= 45,000 J• 1b) Momentum = mv = (400) x (15)

= 6,000 kgm/s• 2a) KE = ½mv2 = 1248 J• 2b) Reduced by a quarter as KE is

proportional to v2.• 2c) Momentum = mv = 312 kgm/s

Marking Homework

• 3a)

• 3b) Momentum =mv = 70x5 = 350 kgm/s• 3c) Momentum =mv = -50x5= -350 kgm/s• 3d) 350 – 350 = 0

70 kg 50 kg

5 m/s 7 m/s

Marking Homework

• 4a) 60,000 kgm/s• 4b) 900,000 J• 4c) 0 kgm/s• 4d) 0 J• 4e) 60,000 kgm/s• 4f) 900,000 J• 4g) 40,000 kgm/s• 4h) 400,000 J

30 m/s

0 m/s

Before the crash:

After the crash:

20 m/s20 m/s

Marking Homework

• 4i) 20,000 kgm/s• 4j) 200,000 J• 4k) 40,000 + 20,000

= 60,000 kgm/s• 4l) 400,000+200,000

= 600,000 J• 4m) The same

• 4n) Lost as heat + sound and changed into elastic potential energy in the deformed metal.

30 m/s

0 m/s

Before the crash:

After the crash:

20 m/s20 m/s