P5 Investigating Motion (page 213)

Question 1

Explain how you set up the experiment that tests Newton’s 2nd law, F = ma (p.211)

Answer 1

1) set up the apparatus shown in diagram 1 p.213.

You set up the trolley so it holds a piece of card with a gap in the middle that will interruupt the signal on the light gate twice.

(if you measure the length of each bit of card that will pass through the light gate and input this into the software, the light gate can measure the velocity of each bit of card. It can use this to work out the acceleration of the trolley.

Question 2

After the apparatus for newton’s 2nd law is set up correctly, you connect the trolley to what?

Answer 2

You connect the trolley to a piece of string that goes over a pulley and is connected on the other side to a hook (that you know the mass of and can add more masses to).

Question 3

Now the trolley is connected to the piece of string for newtons 2nd law experiment appratus, the weight of the hook and any masses attached to it will provice what force?

Answer 3

this will provide the accelerating force, equal to the mass of the hook (m) x acceleration due to gravity (g).

Question 4

Once the accelerating force is happening in newtons 2nd law experiment, the weight of the hook and masses accelerates both the trolley and the masses, why?

Answer 4

so you can investigate the acceleration of the system (the trolley and the masses together).

Question 5

With Newtons 2nd law experiment, where do you mark a starting line?

Answer 5

mark a starting line on the table the trolley is on, so that the trolley always travels the same distance to the light gate.

Question 6

with Newtons 2nd Law experiment, after marking a starting line on the table, what is next?

Answer 6

place the trolley on the starting line, holding the hook so the string is taut (not loose) and touching the table) and release it.

Question 7

with newtons 2nd law experiment, after releasing the string, what do you record?

Answer 7

you record the acceleration measured by the light gate as the trolley passes through it. This is the acceleration of the whole system.

Repeat the experiment twice more to get an average acceleration.

Question 8

How do you investigate the effect of mass? (with newtons 2nd law experiment)

Answer 8

add masses to the trolley one at a time to increase the mass of the system. Don’t add masses to the hook or you’ll change the force. Record the average acceleration for each mass.

Question 9

with newton’s 2nd law experiment, how do you investigate the effect of force?

Answer 9

you need to keep the total mass of the system the same, but change the mass on the hook. To do this, start with all the masses loaded onto the trolley, and transfer the masses to the hook one at a time, to increase the accelerating force (the weight of the hanging masses). The mass of the system stays the same as you’re only transferring the masses from one part of the system (the trolley) to another (the hook). Record the average acceleration for each force.

Question 10

With newton’s 2nd law experiment, the friction between the trolley and the bench might affect your acceleration measurements, how could you reduce this friction?

Answer 10

you could use an air track to reduce this friction (a trace which hovers a trolley on jets of air).

Question 11

How can Newton’s second Law be written?

Answer 11

F = ma

F = Weight of the hanging masses
m = mass of the whold system
a = acceleration of the system.

Question 12

with newtons second law experiment, by adding masses to the trolley, the mass of the whole system increases, but what force is applied to the system?

Answer 12

the force applied stays the same. This should lead to a decrease i the acceleration of the trolley, as
a = F ÷ m

Question 13

with newtons second law experiment, by transferring masses to the hook, you are increasing the accelerating force without changing the mass of the whole system, what will happen?

Answer 13

increasing the force should lead to an increase in the acceleration of the trolley.

Question 14

Explain how a light gate can be used to measure the acceleration of a trolley? (3 marks)

Answer 14

A piece of card with a gap in the middle is attached to the trolley, so that two bits of card stick up and interrupt the light gate beam as it moves (1 mark). The length of each bit of card is input into the light gate software, and the light gate measures the velocity of each bit of card as the trolley moves (1 mark). It can use the two velocity values to find the acceleration (1 mark).