You are Here: Home >< Physics

# Circular motion questions help please! watch

1. A bug of mass 20 mg sits near the edge of a long play (LP) record, at a distance 15 cmfrom the centre. The record player is turned on and the record brought up to its
normal speed of rpm (rev/min). Calculate the minimum value of the coefficientof friction between the bug and the record if the bug does not slip off the record.
Total Marks [9]

2. A truck of total mass 2000 kg travelling at a speed of 15 ms-1, goes over an archedbridge which has a radius of curvature equal to 25 m. Calculate:
1. a) The contact force on the truck when the truck is at the top of the arch. [6]
2. b) The maximum speed at which the truck could safely pass over the bridge, such
that it just loses contact with the road. [4]Total Marks [10]

3.
a) Starting from Newton’s Law of Universal Gravitation show that the orbital period
of a satellite of mass , at a distance from the centre of a planet of mass isgiven by:
where is the universal gravitational constant. [6]b) Use the following data for Mars and Phobos, one of the Moons of Mars, to
calculate:

1. i) the orbital period of Phobos, giving your answer in hours. [6]
2. ii) the escape velocity from Phobos. [3]
Radius of Mars = 3 390 kmMass of Mars = 6.4169 x 1023 kg
Mean radius of Phobos = 11.1 km
Mass of Phobos = 1.0659 x 1016 kg
Mean orbital height above the Martian surface = 5 987 km
Total Marks [15]

4. A spring is stretched 4cm when a mass of 50g is hung on to it. A total mass of 150gis now hung on the end of the spring and displaced so that it performs small verticaloscillations. Calculate the period of these oscillations.
Total Marks [8]

I've got so far with each question but then end up stuck at some point or another, could anyone offer any help/tips please? Thanks
1. Welcome to TSR physics.

Show us how far you've got and at what point you are stuck.

What equations do you know that relate to circular motion?
2. (Original post by Stonebridge)
Welcome to TSR physics.

Show us how far you've got and at what point you are stuck.

What equations do you know that relate to circular motion?
I know the formulas for angular displacement, angular velocity and centripetal force
3. So let's look at Q2

How far have you got with that one using the idea of the centripetal force on the truck?
Where are you stuck?
4. (Original post by Stonebridge)
So let's look at Q2

How far have you got with that one using the idea of the centripetal force on the truck?
Where are you stuck?
I have completed part a and obtained an answer of 1620N.
mv^2/r = mg - R
R = mg - mv^2/r
R = (2000 x 9.81) - (2000x15^2 / 25) = 1620N

Is this correct?
I am struggling with part b and not really sure how to go about it
5. (Original post by rjnknr)
I am struggling with part b and not really sure how to go about it

At the point where it's just about to come off, Fc = weight

Equate the equations and solve for v

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 7, 2015
Today on TSR

### 'I missed the UCAS deadline!'

Here's what to do next...

### University open days

• University of East Anglia
All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
Wed, 30 Jan '19
• Solent University
Sat, 2 Feb '19
• Sheffield Hallam University