# Mechanics

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A firework takes off from ground level, accelerating upwards for 10s with constant acceleration 4m/s^2.

Sketch the displacement time graph.

So I did u= 0, so v= u+at, v= 40m/s, s=vt-1/2at^2, s=200m. Is this correct way of doing the calculation?

Sketch the displacement time graph.

So I did u= 0, so v= u+at, v= 40m/s, s=vt-1/2at^2, s=200m. Is this correct way of doing the calculation?

Last edited by Shas72; 4 weeks ago

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#2

(Original post by

A firework takes off from ground level, accelerating upwards for 10s with constant acceleration 4m/s^2.

Sketch the displacement time graph.

So I did u= 0, so v= u+at, v= 40m/s, s=vt-1/2at^2, s=200m. Is this correct way of doing the calculation?

**Shas72**)A firework takes off from ground level, accelerating upwards for 10s with constant acceleration 4m/s^2.

Sketch the displacement time graph.

So I did u= 0, so v= u+at, v= 40m/s, s=vt-1/2at^2, s=200m. Is this correct way of doing the calculation?

I'd use to get points for the sketch.

Last edited by RogerOxon; 4 weeks ago

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(Original post by

Where did the v=40 and s=200 come from?

**RogerOxon**)Where did the v=40 and s=200 come from?

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(Original post by

Where did the v=40 and s=200 come from?

I'd use to get points for the sketch.

**RogerOxon**)Where did the v=40 and s=200 come from?

I'd use to get points for the sketch.

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#5

(Original post by

By using v=u+at

**Shas72**)By using v=u+at

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(Original post by

You don't need to calculate v before s. As per my edit above:

You should be able to deduce its shape from the equation.

**RogerOxon**)You don't need to calculate v before s. As per my edit above:

You should be able to deduce its shape from the equation.

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**RogerOxon**)

You don't need to calculate v before s. As per my edit above:

You should be able to deduce its shape from the equation.

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#8

(Original post by

Iam not having problems in plotting or sketching the graph. My problem is I'm not able to understand what formulas to use to get to the values

**Shas72**)Iam not having problems in plotting or sketching the graph. My problem is I'm not able to understand what formulas to use to get to the values

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#9

(Original post by

So is it that we know u=0 in this case, t=10s and A= 4m/s^2, so we make use of the formula that has these ?

**Shas72**)So is it that we know u=0 in this case, t=10s and A= 4m/s^2, so we make use of the formula that has these ?

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(Original post by

You are asked to sketch a time-displacement graph, i.e. t and s. You know that u=0 (t=0). You want the simplest formula for s, when you know u, a and t.

**RogerOxon**)You are asked to sketch a time-displacement graph, i.e. t and s. You know that u=0 (t=0). You want the simplest formula for s, when you know u, a and t.

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(Original post by

Yes. Look through the equations that you have, and see which is the most direct for what you want. When u=0, that simplifies many of them.

**RogerOxon**)Yes. Look through the equations that you have, and see which is the most direct for what you want. When u=0, that simplifies many of them.

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#12

(Original post by

Thanks that was very helpful. I was doing all unnecessary stuff of finding v

**Shas72**)Thanks that was very helpful. I was doing all unnecessary stuff of finding v

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(Original post by

Good. It should simplify to the same forumula, but will add extra steps, with the associated possibility of mistakes.

**RogerOxon**)Good. It should simplify to the same forumula, but will add extra steps, with the associated possibility of mistakes.

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**RogerOxon**)

Good. It should simplify to the same forumula, but will add extra steps, with the associated possibility of mistakes.

A ball is thrown upwards from a point 1m above the ground with initial speed 5m/s. It accelerates downwards at a constant rate of 10m/s^2 until it stops moving upwards, when it is caught by someone standing on a ladder.

Sketch the graph

According to what you have advised, s=1m, u=5m/s, a=10m/s^2, v=0 as it stops.

Should I use the same formula?

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#16

(Original post by

Can you pls advise on this one .

A ball is thrown upwards from a point 1m above the ground with initial speed 5m/s. It accelerates downwards at a constant rate of 10m/s^2 until it stops moving upwards, when it is caught by someone standing on a ladder.

Sketch the graph

According to what you have advised, s=1m, u=5m/s, a=10m/s^2, v=0 as it stops.

Should I use the same formula?

**Shas72**)Can you pls advise on this one .

A ball is thrown upwards from a point 1m above the ground with initial speed 5m/s. It accelerates downwards at a constant rate of 10m/s^2 until it stops moving upwards, when it is caught by someone standing on a ladder.

Sketch the graph

According to what you have advised, s=1m, u=5m/s, a=10m/s^2, v=0 as it stops.

Should I use the same formula?

You also need to be careful about where you're measuring s from. All SUVAT equations implicitly have s=0 at t=0.

There are different ways of approaching this - it's all about the one that is simplest or makes the most sense to you.

As your goal is to sketch the graph, and you know that the ball is caught when v=0 (vertically), you can quickly get the time for that. Can you see how?

I would use that time to calculate s. Which SUVAT equation (knowing u, v=0, a and t) is the simplest?

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(Original post by

Be careful with your signs. The acceleration and initial speed are in different directions.

You also need to be careful about where you're measuring s from. All SUVAT equations implicitly have s=0 at t=0.

There are different ways of approaching this - it's all about the one that is simplest or makes the most sense to you.

As your goal is to sketch the graph, and you know that the ball is caught when v=0 (vertically), you can quickly get the time for that. Can you see how?

I would use that time to calculate s. Which SUVAT equation (knowing u, v=0, a and t) is the simplest?

**RogerOxon**)Be careful with your signs. The acceleration and initial speed are in different directions.

You also need to be careful about where you're measuring s from. All SUVAT equations implicitly have s=0 at t=0.

There are different ways of approaching this - it's all about the one that is simplest or makes the most sense to you.

As your goal is to sketch the graph, and you know that the ball is caught when v=0 (vertically), you can quickly get the time for that. Can you see how?

I would use that time to calculate s. Which SUVAT equation (knowing u, v=0, a and t) is the simplest?

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reply

**RogerOxon**)

Be careful with your signs. The acceleration and initial speed are in different directions.

You also need to be careful about where you're measuring s from. All SUVAT equations implicitly have s=0 at t=0.

There are different ways of approaching this - it's all about the one that is simplest or makes the most sense to you.

As your goal is to sketch the graph, and you know that the ball is caught when v=0 (vertically), you can quickly get the time for that. Can you see how?

I would use that time to calculate s. Which SUVAT equation (knowing u, v=0, a and t) is the simplest?

0

reply

**RogerOxon**)

Be careful with your signs. The acceleration and initial speed are in different directions.

You also need to be careful about where you're measuring s from. All SUVAT equations implicitly have s=0 at t=0.

There are different ways of approaching this - it's all about the one that is simplest or makes the most sense to you.

As your goal is to sketch the graph, and you know that the ball is caught when v=0 (vertically), you can quickly get the time for that. Can you see how?

I would use that time to calculate s. Which SUVAT equation (knowing u, v=0, a and t) is the simplest?

I get s=1.25m

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reply

**RogerOxon**)

Be careful with your signs. The acceleration and initial speed are in different directions.

You also need to be careful about where you're measuring s from. All SUVAT equations implicitly have s=0 at t=0.

There are different ways of approaching this - it's all about the one that is simplest or makes the most sense to you.

As your goal is to sketch the graph, and you know that the ball is caught when v=0 (vertically), you can quickly get the time for that. Can you see how?

I would use that time to calculate s. Which SUVAT equation (knowing u, v=0, a and t) is the simplest?

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reply

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