You are Here: Home >< Maths

# Mechanics M1(Momentum) watch

1. I do not get this question at all. I ahd several attempts but none of them worked. Please help!! Here's the question:

A test is carried out on a rocket, of mass 200kg, which is fired horizontally at a speed of 50ms-1. The rocket experiences a constant air resistance force of 1568N. It travels a distance of 108m before it hits a stationary tank, of mass 4800kg. Assume that the rocket always travels horizontally.
(a) Find the speed of the rocket when it has travelled a distance of 108m.
when the rocket hits the tank it becomes lodged in it.
(b) Find the speed of the tank and the rocket just after the collision.
2. f=ma
-1568=200*a
get a then use suvat
part b
momentum before=mom after

(Original post by Sid.)
I do not get this question at all. I ahd several attempts but none of them worked. Please help!! Here's the question:

A test is carried out on a rocket, of mass 200kg, which is fired horizontally at a speed of 50ms-1. The rocket experiences a constant air resistance force of 1568N. It travels a distance of 108m before it hits a stationary tank, of mass 4800kg. Assume that the rocket always travels horizontally.
(a) Find the speed of the rocket when it has travelled a distance of 108m.
when the rocket hits the tank it becomes lodged in it.
(b) Find the speed of the tank and the rocket just after the collision.
3. (Original post by angrypoliceman)
f=ma
-1568=200*a
get a then use suvat
part b
momentum before=mom after
I did use "F=ma" and found a=7.84 and then I used v^2=u^2 + 2as where
s=108
u=50
v=0
a=7.84
but it turns out to be incorrect.
4. (Original post by Sid.)
I did use "F=ma" and found a=7.84 and then I used v^2=u^2 + 2as where
s=108
u=50
v=0
a=7.84
but it turns out to be incorrect.
a should be negative
5. (Original post by angrypoliceman)
a should be negative
Sorry, I dont get why it would be negative
6. (Original post by Sid.)
Sorry, I dont get why it would be negative
It's slowing down ...
7. (Original post by Sid.)
Sorry, I dont get why it would be negative
its decelerating man
8. (Original post by angrypoliceman)
f=ma
-1568=200*a
get a then use suvat
part b
momentum before=mom after
why are you saying the unbalanced force is -1568, it says the resistance force it 1568N. For there to be acceleration there needs to be a thrust force greater than that, but that hasn't been given in the equation.
9. I'm really sorry but I still don't get how would it slow down cause it travels a distance of 108m before it hits a stationary tank, of mass 4800kg. please explain to me!
10. (Original post by NGEO)
why are you saying the unbalanced force is -1568, it says the resistance force it 1568N. For there to be acceleration there needs to be a thrust force greater than that, but that hasn't been given in the equation.
You have just confused me now!
11. (Original post by NGEO)
why are you saying the unbalanced force is -1568, it says the resistance force it 1568N. For there to be acceleration there needs to be a thrust force greater than that, but that hasn't been given in the equation.
im saying the resultant force is -1568 since theres no forward force on the rocket and a drag force
12. (Original post by Sid.)
Sorry, I dont get why it would be negative
Because the rocket is decelerating , the force in the f=ma equation should be negative as the resultant force is negative (F=0-1568)
(you should get one direction as positive and one direction as negative when first starting the problem)

so for f=ma is -1568=200a
13. (Original post by Sid.)
You have just confused me now!
listen to the guy who got an E in mechanics dude. I know my ****
14. (Original post by angrypoliceman)
im saying the resultant force is -1568 since theres no forward force on the rocket and a drag force
Ahhh sorry, i forgot that rocket can slow down. silly me

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: October 25, 2017
Today on TSR

### Uni league tables

Do they actually matter?

### University open days

• University of Exeter
Wed, 24 Oct '18
Wed, 24 Oct '18
• Northumbria University
Wed, 24 Oct '18
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

## Groups associated with this forum:

View associated groups

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