You are Here: Home >< Maths

# M1 help needed urgently!! watch

1. A test is carried out on a rocket, of mass 200kg, which is fired horizontally at a speed 50m p/s. The rocket experiences a constant air resistance force of 1568 N. It travels a distance of 108m before it hits a stationary tank, of mass 4800kg. Assume 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 into it:

b) Find the speed of the tank and the rocket just after the collision ( i can probably do this with the conservation of momentum, but i need part a) to do it!)

The tank then slides until it comes to rest. The coefficient of friction is 0.6 between the tank and the ground. Neglect air resistance.

c) find the distance that the tank slides.

Any help would be much appreciated, have got M1 exam tomorrow, and everything was going well....until now...
2. a)
Two ways of doing it. I'll do the simplier longer way first.
F= ma
a = 1568/200 = 7.84ms-2
v^2 = u^2 + 2as
Since a is in the opposite direction to s a is negative.
v^2 = 50^2 +2 x 108 x -7.84
v^2 = 2500 - 1693.44
v^2 = 806.56
v = 28.4ms-1

Alternatively
E = Fs
1/2mv^2 = E
1/2mv^2 = 1/2mu^2 - Fs
v^2 = u^2 - 2Fs/m
Which gives the same equation as above.

b) Assume inelastic collision.
200u = (200+4800)v
v = 200 x 28.4/5000
v = 1.136m/s

c) F = mju R
Assume the rocket becomes part of the tank, hence R = 5000g
F = ma
ma = mju m g
a = mju g (hmm...mju g....that shop...OooO)
v^2 = u^2 + 2as
0 = u^2 +2as
2 mju g s = u^2
s = 1/2 u^2 /mju /g
s = 0.1096m
3. ahh, thanks, i just wasnt sure whether a = 1568/200 or whether there was another force driving the rocket forwards, ie whether F - 1568 = 200a, or as you said 1568 = 200a.

Thanks for clearing that up - did you just realise there was no other force acting other than the air resistance, how did you know that? This always confuses me, how is the rocket moving forwards then? if theres no force going forwards, only one going backwards? Thanks for you help! x
4. Mr = 200 kg
Mt = 4,800 kg
u = 50 m/s
R =1568 N

a)
R = Mr*d
d = 1568/200
d = 7.84 m/s²
===========

v² - u² = 2as
v² - 50² = -2*7.84*108
v² = 2500 - 1693.44
v² = 806.56
v = 28.4 m/s
==========

b)
Mr.v = (Mr + Mt)v'
v' = (200*2.84) / (200 + 4800) = 200*28.4/5000
v' = 1.136 m/s
===========

c)
Neglecting air resistence,

Fr = µ.NR = 0.6*5000*g = 29,400 N

Fr = (5000)*d2
d2 = 29,400/5000 = 5.88 m/s²

v² - u² = 2as
s = 1.136²/(2*5.88)
s = 0.1097 m
s = 11 cm
========
5. (Original post by xXxKatiexXx)
ahh, thanks, i just wasnt sure whether a = 1568/200 or whether there was another force driving the rocket forwards, ie whether F - 1568 = 200a, or as you said 1568 = 200a.

Thanks for clearing that up - did you just realise there was no other force acting other than the air resistance, how did you know that? This always confuses me, how is the rocket moving forwards then? if theres no force going forwards, only one going backwards? Thanks for you help! x
This is a created situation.
A rocket is (somehow) given a speed of 50 m/s.
Your also told that the rocket travels horizontally. (which doesn't happen in practice) This is just to simplify thngs..

You're not told in the question that there is any other force acting, so assume none.
Assume that the rocket has a constant speed, that there is no propulsive force (none mentioned), and a constant resistence slowing it down from the starting speed.

Your problem is then to figure out what happens afterwards

Always watch out for gravity effects though! That means a force is acting.
6. thanks everyone - i think i was just making everything much more complicated than it needed to be! Wish me luck!

### 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: June 15, 2005
The home of Results and Clearing

### 1,789

people online now

### 1,567,000

students helped last year
Today on TSR

### Took GCSEs this summer?

Fill in our short survey for Amazon vouchers!

### University open days

1. University of Buckingham
Thu, 23 Aug '18
2. University of Glasgow
Tue, 28 Aug '18
3. University of Aberdeen
Tue, 28 Aug '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