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Explore and Calculate Momentum

Worksheet Overview

QUESTION 1 of 10

Ever tried to stop a train with a feather? Do you think you'd be able to do it? Is it a stupid question? Yes, it is, but more interestingly is why a feather cannot stop a train. Most of you will say it is because of its mass - and you'd be sort of correct. Did you know, however, that if you shot a feather quick enough, theoretically it would be able to stop a train?  This is something to do with momentum -  let's look at what momentum is now. 

 

Moving objects have momentum. The more momentum an object has, the harder it is to change its direction. To calculate momentum you need to use the following formula:


momentum (kg m/s) = mass (kg) × velocity (m/s)


Total momentum stays the same in explosions and collisions, as long as no external forces act on the objects involved. When a car travels, everything in it has momentum so that in the event of a crash, forces act on passengers in the car and this can cause injury. If the time taken to change the momentum is increased, the forces on the bodies of the passengers reduce. This is the purpose of seat belts, crumple zones and air bags.

To calculate the force involved in changing momentum, you can use the following equation:


Equation for changing momentum.

 

Are you ready for those questions now?

What do all moving objects have? Consider the Introduction and write the word in the answer box below.

Is the following statement true or false?

 

The more momentum an object has, the harder it is to change its direction.

True

False

What happens to the total momentum in explosions and collisions, as long as no external forces act on the objects involved?

It decreases

It increases

It stays the same

Calculate the momentum of an object if it has a mass of 80 kg and moves with a velocity of 60 m/s.

It decreases

It increases

It stays the same

Calculate the momentum of an object if it has a mass of 100 kg and moves with a velocity of 3 m/s.

300 kg m/s

3000 kg m/s

30 kg m/s

How can the forces acting on passengers in a car be reduced to avoid injury in the case of an accident? 

Increase the time taken to change the momentum

Reduce the time taken to change momentum

Wear a seat belt

Move your seat forward

Which of the features listed below are important for car safety?

Crumple zones

Windscreen

Steering wheel

Air bags

What do you need to divide the change in momentum by to get the force needed to change it?

By the change in the forces acting on the system

By the time taken for change

By the momentum of all subjects and objects involved

A bullet with a mass of 0.05 kg leaves a gun at 2000 m/s.

 

If the gun’s mass is 2 kg, what is the velocity of the recoil on the gun?

150 m/s

200 m/s

50 m/s

A 15 kg bicycle is travelling at 10 m/s. What force is needed to bring it to a halt in 3 s?

50 N

100 N

150 N

  • Question 1

What do all moving objects have? Consider the Introduction and write the word in the answer box below.

CORRECT ANSWER
momentum
EDDIE SAYS
Did you get that right? There were all sorts of things you might have thought of putting such as wheels, brakes etc but in fact not all moving objects have these things. What is this activity about? There's a bit of a clue! All moving objects have momentum.
  • Question 2

Is the following statement true or false?

 

The more momentum an object has, the harder it is to change its direction.

CORRECT ANSWER
True
EDDIE SAYS
The statement is true - the more momentum an object has, the harder it is to change its direction. Have you ever seen a dog or a cat running really fast; the momentum is so great that the animal often skids or trips over when it tries to change direction!
  • Question 3

What happens to the total momentum in explosions and collisions, as long as no external forces act on the objects involved?

CORRECT ANSWER
It stays the same
EDDIE SAYS
A hard one this - how did you get on with it? The total momentum in explosions and collisions stays the same, as long as no external forces act on the objects involved.
  • Question 4

Calculate the momentum of an object if it has a mass of 80 kg and moves with a velocity of 60 m/s.

CORRECT ANSWER
EDDIE SAYS
Now you've got the chance to do a wonderful equation! Can you remember what the formula is? Here we go: momentum = mass × velocity The mass = 80 kg The velocity is 60 m/s So, the momentum = 80 x 60 = 4800 kg m/s
  • Question 5

Calculate the momentum of an object if it has a mass of 100 kg and moves with a velocity of 3 m/s.

CORRECT ANSWER
300 kg m/s
EDDIE SAYS
Here's another chance to use that wonderful equation: momentum = mass × velocity Mass = 100 kg Velocity = 3 m/s Momentum = 100 x 3 = 300 kg m/s
  • Question 6

How can the forces acting on passengers in a car be reduced to avoid injury in the case of an accident? 

CORRECT ANSWER
Increase the time taken to change the momentum
Wear a seat belt
EDDIE SAYS
This was a tricky one - which was correct out of the first two options? The forces acting on passengers in a car can be reduced to avoid injury by increasing the time taken to change the momentum, which is achieved by wearing a seat belt.
  • Question 7

Which of the features listed below are important for car safety?

CORRECT ANSWER
Crumple zones
Air bags
EDDIE SAYS
Two features of car safety are crumple zones and airbags. They slow you down with the car, dissipating your momentum and making it safe for you to stop.
  • Question 8

What do you need to divide the change in momentum by to get the force needed to change it?

CORRECT ANSWER
By the time taken for change
EDDIE SAYS
This was a really tricky question - did you understand it? The way to grasp this is to look at the equation given in the Introduction. Force = change in momentum ÷ time taken for change You need to divide the change in momentum by the time taken for the change to happen. This equation will not be given to you in an exam - so remember it.
  • Question 9

A bullet with a mass of 0.05 kg leaves a gun at 2000 m/s.

 

If the gun’s mass is 2 kg, what is the velocity of the recoil on the gun?

CORRECT ANSWER
50 m/s
EDDIE SAYS
This looks really complicated but it is really just giving us a chance to use that wonderful equation! First of all, we need to find the momentum of the bullet: Momentum = mass x velocity So, momentum = 0.05 x 2000 = 100 kg m/s Next, we need to rearrange the equation so that we can find out the velocity of the recoil on the gun: Velocity = momentum ÷ mass So. velocity = 100 ÷ 2 = 50 m/s Phew, well done for working through all of that!
  • Question 10

A 15 kg bicycle is travelling at 10 m/s. What force is needed to bring it to a halt in 3 s?

CORRECT ANSWER
50 N
EDDIE SAYS
This looks really complicated but just work it through slowly, one bit at a time and you'll get there. First of all, we need to work out what the momentum was at the start, so use the equation: momentum = mass x velocity So, momentum at start = 15 x 10 = 150 kg m/s Next, you need to work out the momentum at the end: Momentum at end = 15 x 0 ( it is no longer moving!) = 0 kg m/s So the change in momentum = 150 - 0 = 150 kg m/s Now we need to use the other equation: force = change in momentum ÷ time taken to make change So, force = 150 ÷ 3 = 50 N Well done if you worked this through and got the correct answer! Great work for completing another activity - you're ticking off that physics!
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