Circular Motion

Question 1

Give the equation for finding radians from degrees

Answer 1

Angle in radians= pi/180 x angle in degrees

Question 2

Define angular velocity

Answer 2

The rate of change of an angle

Question 3

Define centripetal force

Answer 3

A force that acts perpendicular to the motion of an object therefore towards the centre of the circular path followed by the object

Question 4

Give the equation for angle of velocity in terms of theata and time

Answer 4

W=theata/time

Question 5

A satellite is in a circular orbit around the Earth. Explain why the velocity of the satellite changes as it orbits the Earth

Answer 5

Because gravity causes the satellite to accelerate constantly and the acceleration causes a change in direction therefore velocity changes as the direction changes

Question 6

Define one radian

Answer 6

The ark links divided by the radius of the Circle

Question 7

What is the unit for angular velocity?

Answer 7

Radiance per second

Question 8

Convert 4500 RPM into RPS

Answer 8

It’s revolution per minute therefore instead of multiplying by 60 you have to divide by 60
Therefore 4500 RPM is 75 RPS

Question 9

How do centripetal force and velocity act

Answer 9

They are perpendicular to eachother, centripetal force is the resultant of other forces acting on. The object

Question 10

A stone is spun using a string why is it moving in a circle, the forces acting on it are weight tension and centripetal force

Answer 10

There is a resultant force acting toward the centre of the circle provided by the weight and the tensin, tension i pointing toward centre of circle, the resultant force is the centripetal force

Question 11

A satellite is orbiting the earth it has a centripetal force, state 2 factors determining the size of this force

Answer 11

The velocity of the satellite
The radius of the orbit

Question 12

A student is using a string attached to a bung and spinning it, the bung has a centripetal force, in which direction does the force act, the bung is spinning in a circle

Answer 12

Towards the centre of the circle

Question 13

A student is spinning a string attached to a bung, it is moving in a circle and has a centripetal force, what would happen if the string snapped at the moment when the string and the bung is parallel to the floor

Answer 13

The bung wld continue moving in a straight line at constant velocity in the direction it is moving in as there is no resultant force

Question 14

What must be true for an object to follow a circular path

Answer 14

There must be a net force acting towards the centre of the circle (centripetal force)
This must be constant to cause an acceleration

Question 15

An aircraft is travelling in a circle, what effect would increasing the weight of the plane do to the centripetal force, and what effect would reducing the velocity of the plane do to its centripetal force

Answer 15

Weight- the CF increases to keep the plane moving at a constant radius
Velocity- CF reduces to keep plane flying at a constant radius

Question 16

A student wishes to test the equation F=mv^2/r for a constant force F using a whirling bung, how can this experiment be conducted to find the validity of this equation

Answer 16

Whirl a cord attached to a bung in a circle , use a stopwatch to time the time taken for 10 oscillations, then divide by 10 to find the time for 1 oscillation, then find mean , then find T^2
Use a ruler to measure the length of string=r, repeat for diff r
Sub F=mv^2/r with v=2pir/T to get F= 4pi^2mr/T^2
Then plot T^2 against r, if equation is valid it wld be a straight line through the origin

Question 17

What is the fourth causing the circular path of an electron orbiting a nucleus?

Answer 17

The electrostatic force pulling the electron to the centre

Question 18

What is the force causing the circular path of a plane moving in a circle in the air?

Answer 18

The lift force

Question 19

What is the force causing a car to travel in a circular path?

Answer 19

The friction

Question 20

Name the type of acceleration when an objects is moving in a circle and stated direction

Answer 20

Centripetal acceleration
Towards the centre of the circle

Question 21

How do you find the absolute uncertainty of a calculated value using percentage uncertainty?

Answer 21

Percentage uncertainty divided by 100 times the measured value

Question 22

A suitcase is travelling on a conveyor belt in a straight line. It has a fictional force F and a normal reaction force R the suitcase then travels around a curve. Explain why the suitcases frictional force increases and its reaction force decreases whilst it’s travelling around a curve.

Answer 22

The suitcase velocity is changing as its direction is changing constantly therefore the suitcase accelerates there is a result of force acting towards the centre of the circle. This is a centripetal force provided by the friction therefore the friction force is larger whilst it is travelling around the bend would then have to decrease the weight.

Question 23

A bowl of mass 0.3 kg is attached to a string and moves in a vertical circle of radius 0.6 m at a constant speed of 5 m/s maximum and minimum tension in the string

Answer 23

Maximum tension is when the ball is at the bottom of the vertical circle therefore the tension would equal the centripetal force plus the weight
Minimum tension is when the ball is at the top of the circle so the tension equals the centripetal force minus the weight
F=12.5 using formula
Therfore max= 12.5 + 9.81(0.3) = 15
Min= 12.5 - 9.81(0.3) = 9.6

Question 24

A string is passed through a smooth thin tube it has a mass of M attached to the string on the bottom of the tube perpendicular to the floor and a mass m which is r metres away from the tube the tube is moved so that the mass m moves in a horizontal circle of constant radius r and add constant speed v write an expression which is equal to M

Answer 24

The tension is providing the centripetal force and tension is provided by the Mass M therefore Mg = mv^2/r
Therefore M= mv^2/rg

Question 25

A ball is swung around on the end of a string so that the ball moves in a horizontal circle with constant speed discuss the motion of the ball in terms of the forces that act on it include newtons three laws of motion applies to its motion in a circle. Explain why impact the string will not be horizontal.

Answer 25

Newton’s first law= the ball is not travelling in a straight line therefore there is a resultant force acting on it. It is travelling at constant speed however it is accelerating as the direction is changing. Therefore velocity is also changing.
Newton second law = the fourth on the ball causes the ball to accelerate in the direction of the force. This sport is the centripetal force which acts towards the centre of the circle therefore the acceleration of the ball act towards the centre of the circle.
Newton third law = the ball pools on the central point of support with a force opposite to the force pulling the ball from the centre
The ball is supported and swings around in a horizontal circle in practice because the rope is not horizontal as when the rope is horizontal. The weights component is too large and the ball drop therefore the component is given by the vertical component of tension which is action towards the centre of the circle and the horizontal component of detention gives us a central force.

Question 26

A hammer thrower launches a ball attached to a wire by rotating his body about a vertical axis, assuming the ball is moving at a constant speed in a horizontal circle explain why in practice the throwers hand can not be parallel to the ground

Answer 26

The force exerted by the wire on the ball must include a vertical component this is given by Tcostheta