You are Here: Home >< Physics

# Edexcel As Level New syllabus questions, Unit 1: MECHANICS Watch

1. i have some questions and was wondering if anyone could help me with these please!! Some of these questions have been in my head since O'levels. and that's why i got a B in it, i want to make up for the B in a'levels.

Q1. Define Displacement?

Q2. Give examples where the centre of gravity and centre of mass are different?

Q3. When a monkey drops from a branch at the same time a bullet is fired horizontally at it, the bullet will hit the monkey because they have the same downward acceleration. How come the monkey and bullet have the same downward acceleration? The mass of the monkey is greater so why?

Q4. How come energy has magnitude only when two vector quantities (Newton and Metre) are multiplied to get Joule?

2. 3. W=mg , F=ma. Since weight is the force when falling we can say mg=ma therefore a = g

4. Scalar Product
3. Q1. Define Displacement?
Displacement is the distance moved in a certain direction as displacement is a vector, it is considered as the shortest possible route from a - b. Displacement=average velcoity x time

Q2. Give examples where the centre of gravity and centre of mass are different?
Centre of gravity is where the point at where the entire weight of an object acts. The centre of mass is where the entire mass is said to be concentrated.

Centre of gravity can be considerd in designing cars where the cars weight is dsitrubuted over a longer area and lower down to have better grip.
The centre of mass can be considerd in a ring, where the centre of mass is actually in the centre of the ring, which is in the air.

Q3. When a monkey drops from a branch at the same time a bullet is fired horizontally at it, the bullet will hit the monkey because they have the same downward acceleration. How come the monkey and bullet have the same downward acceleration? The mass of the monkey is greater so why?
I think this question takes into account if air resistance is ingnored, if so referring to newtons second law(its always good to refer to these)F=ma, a=accerleration so if a=F/m then they will fall at the same rate. They will both fall at the same rate as Horizontal and vertical velocities are independent. No matter how fast the bullet is fired horizontally - it still falls at the same rate with the pull of gravity. However the bullet would have a independet distance but it would always impact the target on its course.

Q4.

it is a scalar because it is the dot multiplication or scalar multiplication. Work done= energy, workdone=force x displacment, these are both vector quanaties. scalarxscalar=scalar
scalarxvector=vector. vector*vector=scalar(dot)
4. Q2. Centre of Gravity and Centre of mass will not correspond to the same point in cases where the object is in a non-uniform gravitational field.
5. (Original post by Andrea03)
Q1. Define Displacement?
Displacement is the distance moved in a certain direction as displacement is a vector, it is considered as the shortest possible route from a - b. Displacement=average velcoity/time
That should be displacement = average velocity * time;
6. (Original post by Stonebridge)
That should be displacement = average velocity * time;
Cheers for the heads up i edited it, just got confused thats all. Im studying for the same exam did that all sound right to you?
7. (Original post by Andrea03)
Cheers for the heads up i edited it, just got confused thats all. Im studying for the same exam did that all sound right to you?
Your explanation of displacement is fine. I wouldn't define it as average velocity * time, though.
More the other way round. Average velocity is total displacement / time. (Like average speed = total distance / time)
It can also be defined as "change in position". [In the sense that it is independent of the path taken, and just represents the (spatial) difference between where you finished and where you started]

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: December 26, 2010
Today on TSR

### Oxford grad sues for £1m

Claims damages because he didn't get a first

### 'No evidence of shots fired' at Oxford Circus

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.