Circular Motion

Question 1

When an object is travelling in a circular motion should the free body force diagram be balanced?

Answer 1

When an object is travelling in a circular motion the free body force diagram must not be balanced.

Question 2

What forces act on the person on the ride (on one of those spinny rides)

Answer 2

Only weight and tension - no outwards force.

Question 3

A wet sock in a tumble dryer rotates at 790 revolutions per minute. The radius is 0.27m

Show that the speed of the rim of the drum is 22 ms-1
What is the centripetal acceleration of the sock?
Explain how the sock gets this acceleration

Answer 3

a) 22ms^-1
b) 1800ms^-1
c) The sock gets this centripetal acceleration from the force of the drum wall pushing it inwards towards the centre of rotation

Question 4

A car is moving on a level road at 40mph. I fit is to keep the centripetal acceleration below 9.8ms^-2, what is the ‘tightest’ corner it can turn?

Answer 4

v = 18 ms-1
a = 9.8 ms-2
r = ?
acceleration, a	= velocity2 ÷ radius
		    9.8		> 182 ÷ r
minimum	 r 		= 182 ÷ 9.8		= 33 m

Question 5

A dog is sent to space. It orbits the Earth once every 91.8 mins. The space station it is in has a mass of 21100kg and an orbit radius of 6750km.

Calculate:

a) The dog’s angular speed in orbit
b) The centripetal force on the space station (provided by the pull of gravity).

Answer 5

a) 1.14 x 10^-3 rad s^-1

b) 1.85 x 10^5

Question 6

A bobsleigh of total mass 380 kg is travelling at a speed of 31ms (almost 70 m.p.h.!) along an ice channel. At the moment it is turning a corner that is part of a horizontal circle of radius 46 m and the bobsleigh is tilted to the vertical at an angle of 65°. Assume that friction is negligible.

a) Calculate the centripetal acceleration of the bobsleigh

b) Calculate the centripetal force acting on the bobsleigh
c) Calculate the reaction force R

Answer 6

a) 21ms^-2
b) 8000N
c) 8800N