Momentum

Figure 12 shows a student playing a game called ‘pool’.

In a game of pool, the player hits the white ball with a wooden cue.

Use the Physics Equations Sheet to answer questions 07.1 and 07.2.

Which equation links kinetic energy (E_k), mass (m) and speed (v)?

Tick () one box.

E_k = mv²

At one time during the game, the kinetic energy of the white ball is 0.0441 J.

The mass of the white ball is 0.180 kg.

Calculate the speed of the white ball.

The moving white ball collides with a stationary black ball.

Figure 13 shows the two balls before and after the collision.

Momentum is conserved in the collision.

What is meant by ‘momentum is conserved’?

Determine the velocity of the black ball after the collision. mass of white ball = 0.180 kg

mass of black ball = 0.160 kg

Use the Physics Equations Sheet.

Figure 7 shows two people wearing inflatable bodysuits.

The bodysuits are made of soft plastic and are inflated with air.

The bodysuits reduce the chance of injury in a collision.

Explain how wearing a bodysuit reduces the chance of injury in a collision.

Figure 8 shows person A about to collide with person B.

The arrows show the direction in which each person is moving.

The velocity of person A is + 2.0 m/s.

The two people collide and stop.

Calculate the velocity of person B before the collision.

Use the Physics Equations Sheet.

Figure 9 shows a person in an inflatable sphere rolling down a hill.

The total mass of the person and sphere is 80 kg.

The sphere moves through a vertical height of 6.4 m.

gravitational field strength = 9.8 N/kg

Calculate the maximum possible speed of the sphere at the bottom of the hill.

Use the Physics Equations Sheet.

The actual speed of the sphere at the bottom of the hill is much less than the maximum possible speed.

Explain why.

Figure 10 shows a karate expert breaking a wooden board with one hand.

When the hand hits the wooden board, the initial velocity of the hand is 7.5 m/s.

The change in momentum of the hand is 5.0 kg m/s.

The mass of the hand is 0.80 kg.

Calculate the final velocity of the hand.

Use the Physics Equations Sheet.

As the hand exerts a force on the wooden board, the wooden board exerts a force on the hand.

Explain how Newton’s third law applies to the hand hitting the wooden board.

Figure 11 shows the hand hitting the wooden board. When the hand hits the wooden board, the wooden board bends.

When the hand hits the wooden board, the hand moves through a distance of 1.2 cm while exerting a force on the wooden board.

The work done by the hand is 6.0 J.

Calculate the force the hand exerts on the wooden board.

Use the Physics Equations Sheet.

Figure 9 shows a plan view of the route a car travelled from town P to town Q.

The distance the car travelled is a scalar quantity.

The displacement of the car is a vector quantity.

Describe what is meant by a scalar quantity and a vector quantity.

Determine the displacement of the car when the car has travelled from town P to town Q.

At town Q, the car collided with a stationary van.

Figure 10 shows the two vehicles before and after the collision.

Total momentum was conserved in the collision.

mass of car = 1250 kg mass of van = 3000 kg

Calculate the speed v of the van after the collision.

Ten-pin bowling is a game where a ball is rolled along the floor to knock over some wooden pins.

Figure 8 shows a person ten-pin bowling.

The person applied a mean force of 198 N to the ball for a time of 0.25 s.

The mass of the ball was 5.5 kg.

Calculate the velocity of the ball just after leaving the person’s hand.

The collision of the ball with the pins is an example of the conservation of momentum.

Explain how.

An athlete takes part in a race on a straight, horizontal running track.

Figure 5 shows the velocity-time graph for the athlete during the race.

What is the main force that opposes the athlete’s forward motion?

Which section of the graph represents a part of the race where the resultant force on the athlete is zero?

Tick one box.

The athlete has a mass of 94.8 kg

Calculate the momentum of the athlete at a time of 6.0 s

Use Figure 5.

The acceleration is not constant from D to E.

Determine the acceleration at a time of 12.0 s

Use Figure 5.

Give the unit.

Figure 6 is a copy of Figure 5 to help you answer the following questions.

A second athlete starts the race at the same time as the first athlete.

The second athlete moves with a constant acceleration of 1.6 m/s² for the first 6.0 seconds of the race.

The first athlete travels further than the second athlete during the first 6.0 seconds.

Draw a line on Figure 6 to represent the motion of the second athlete for the first 6.0 seconds of the race.

Determine the extra distance travelled by the first athlete over the first 6.0 seconds of the race.

Use Figure 6.