You are Here: Home >< Maths

Mechanics 1 projectiles Q watch

1. I have a M1 exam in January and I am very stuck on part 3 and part 4 of this question.

2. (Original post by thegreenchildren)
I have a M1 exam in January and I am very stuck on part 3 and part 4 of this question.

iii) two parts are always the same height because they both (after explosion) have 0ms-1 vertical velocity and accelerate uniformly due to gravity (recall horizontal and vertical components are independent)

because of this, the only difference between the two parts is the horizontal distance between them

now find expressions for the distance travelled by the two parts after time t and the subtract the expressions for the distance between them

iv) plug the times into the above expression to calculate the distance between them for the times when they hit the ground (by symmetry, this is just twice the time it took to reach the maximum)

and the time it takes both to be 10m above the ground (i.e. calculate the time it takes the projectiles to fall 30m using ) and plug it in to the expression
3. (Original post by boner in jeans)
iii) two parts are always the same height because they both (after explosion) have 0ms-1 vertical velocity and accelerate uniformly due to gravity (recall horizontal and vertical components are independent)

because of this, the only difference between the two parts is the horizontal distance between them

now find expressions for the distance travelled by the two parts after time t and the subtract the expressions for the distance between them

iv) plug the times into the above expression to calculate the distance between them for the times when they hit the ground (by symmetry, this is just twice the time it took to reach the maximum)

and the time it takes both to be 10m above the ground (i.e. calculate the time it takes the projectiles to fall 30m using ) and plug it in to the expression
Thank you for your help but I need to ask some questions.

How do you know both parts have 0ms-1 velocity after explosion?

For part 3, I have got two expressions but I don't think they are anything like the answer in the mark scheme. I have s=21t and s=13.125t.
On the markscheme how have they got 0.75x21t=15.75t ?

4. (Original post by thegreenchildren)
Thank you for your help but I need to ask some questions.

How do you know both parts have 0ms-1 velocity after explosion?

For part 3, I have got two expressions but I don't think they are anything like the answer in the mark scheme. I have s=21t and s=13.125t.
On the markscheme how have they got 0.75x21t=15.75t ?

1) well since it explodes instantaneously at the maximum (where the vertical velocity = 0), it can be assumed the only velocity it has is the horizontal component

2) one of the expressions for the displacement is 21t, the other is 1/4 x 21t which should be 5.25t

and 21t - 21/4t is the same as 21t x 0.75

it's alright sweet cheeks
5. (Original post by boner in jeans)
1) well since it explodes instantaneously at the maximum (where the vertical velocity = 0), it can be assumed the only velocity it has is the horizontal component

2) one of the expressions for the displacement is 21t, the other is 1/4 x 21t which should be 5.25t

and 21t - 21/4t is the same as 21t x 0.75

it's alright sweet cheeks
When it says find the distance between the fireworks when they reach the ground, surely the time to reach the ground would be double the time taken to reach the maximum height? But they use the time taken to reach maximum height and multiply it by 15.74?
6. Oh its because they are talking about after the explosion so it takes an equal amount of time to land.

Related university courses

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: January 5, 2013
Today on TSR

Summer Bucket List is Back!

Start yours and you could win £150!

Poll
Useful resources

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

How to use LaTex

Writing equations the easy way

Study habits of A* students

Top tips from students who have already aced their exams

Chat with other maths applicants