# Mechanics

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#1
I'm struggling with these questions and i tried the SUVAT formulas that are appropriate to use. Can anyone help me?

1.
A particle, initially 15 m from the origin and travelling at -2 ms-1, accelerates at a constant rate and ends up -20 m from the origin and travelling at -5 ms-1.

What is its acceleration?

2.A train is timed between successive posts A, B and C, each 2000 m apart. It takes 100 seconds to travel from A to B and 150 seconds to travel from B to C. The acceleration throughout the journey is uniform.

ms-2

Find the velocity of the train at B. Answer
ms-1

(Give your answers as exact whole numbers or decimals or as fractions in their lowest terms in the form p/q).

3.A particle starts from rest and moves in a straight line with constant acceleration. In a certain 4 seconds of its motion it travels 12 m and in the next 5 seconds it travels 30 m.

What is the acceleration of the particle? Answer
ms-2

What is the velocity of the particle at the start of timing? Answer
ms-1

m

(Give your answers as exact whole numbers or decimals, or as fractions in their lowest terms in the form p/q).
0
7 months ago
#2
(Original post by VEMMMM)
I'm struggling with these questions and i tried the SUVAT formulas that are appropriate to use. Can anyone help me?

1.
A particle, initially 15 m from the origin and travelling at -2 ms-1, accelerates at a constant rate and ends up -20 m from the origin and travelling at -5 ms-1.

What is its acceleration?
Let's start here. You need to appreciate that the SUVAT equations implicitly assume that s=t=0 at the point that you specify u.

For each question look at the variables that you have, and select the relevant SUVAT equation. Here you have s, u and v, and want a. Which SUVAT equation has only those variables?
Last edited by RogerOxon; 7 months ago
0
7 months ago
#3
(Original post by VEMMMM)
I'm struggling with these questions and i tried the SUVAT formulas that are appropriate to use. Can anyone help me?

1.
A particle, initially 15 m from the origin and travelling at -2 ms-1, accelerates at a constant rate and ends up -20 m from the origin and travelling at -5 ms-1.

What is its acceleration?

2.A train is timed between successive posts A, B and C, each 2000 m apart. It takes 100 seconds to travel from A to B and 150 seconds to travel from B to C. The acceleration throughout the journey is uniform.

ms-2

Find the velocity of the train at B. Answer
ms-1

(Give your answers as exact whole numbers or decimals or as fractions in their lowest terms in the form p/q).

3.A particle starts from rest and moves in a straight line with constant acceleration. In a certain 4 seconds of its motion it travels 12 m and in the next 5 seconds it travels 30 m.

What is the acceleration of the particle? Answer
ms-2

What is the velocity of the particle at the start of timing? Answer
ms-1

m

(Give your answers as exact whole numbers or decimals, or as fractions in their lowest terms in the form p/q).
Well what exactly have you tried?

Take the 1st equation - which SUVAT equation are you using, and what values are you plugging into it?
0
#4
Orignally i used the equation V=U+AT so -20=15-7a
then i got 35=-7a
meaning a is 5 but intergal maths said the answer is wrong

This is where i am stuck cos i dont know what else to do
(sorry its probably wrong since i had to self isolte during the time we learnt this)
Last edited by VEMMMM; 7 months ago
0
7 months ago
#5
(Original post by VEMMMM)
Orignally i used the equation V=U+AT so -20=15-7a
then i got 35=-7a
meaning a is 5 but intergal maths said the answer is wrong

This is where i am stuck cos i dont know what else to do
(sorry its probably wrong since i had to self isolte during the time we learnt this)
You must realise u and v are velocities, but you've used displacements (15,-20).
List the 4 terms in the question, then pick the suvat equation that relates them together.
0
7 months ago
#6
(Original post by VEMMMM)
Orignally i used the equation V=U+AT so -20=15-7a
then i got 35=-7a
meaning a is 5 but intergal maths said the answer is wrong

This is where i am stuck cos i dont know what else to do
(sorry its probably wrong since i had to self isolte during the time we learnt this)
You should notice that in the equation V=U+AT, V denote the final velocity, but you seems to think it as the displacement. However, even if you use the correct number, calculating acceleration by using this method is still inappropriate, since you have two unknowns in a single equation(T and A). Therefore, trying to find a proper SUVAT equation that can help you to eliminate the # of unknowns to one is important.
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