You are Here: Home >< A-levels

# Mechanics 1 question - momentum watch

1. Stuck on this question:
Three supermarket trolleys, each of mass 20 kg, are placed on a straight line. As these trolleys move they are not subject to any resistance to motion. The first one is set in motion so that it moves at a speed of 4.5 m s–1 towards the second trolley. It then collides with the second trolley. After this collision the two trolleys continue to move together along the straight line at constant speed until they collide with the third trolley. After this collision all three trolleys move together along the straight line.
(a) Show that the speed of the two moving trolleys after the first collision is 2.25 m s–1.
(b) Find the speed of the trolleys after the second collision.
(c) After the second collision the combined trolleys are subject to a single, horizontal resistance force of magnitude 30 N.
(i) Calculate the acceleration of the trolleys while this force acts.
(ii) Find the distance, that the trolleys move after the second collision, before they come to rest.

Have hit a brick wall at part c(i), (got 1.5m/s for b) For c is it just F=MA? If so is F just the 30N or does the 1.5m/s have some part in it?
Thanks
2. Yes, I think it is just F=ma using -30N as the resultant force
(taking the trolleys' direction of motion as the positive direction)

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 26, 2016
The home of Results and Clearing

### 2,130

people online now

### 1,567,000

students helped last year
Today on TSR

### University open days

1. London Metropolitan University
Sat, 18 Aug '18
2. Edge Hill University
Sat, 18 Aug '18
3. Bournemouth University
Sat, 18 Aug '18
Poll

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets