Download Mechanics Revision #1

Mechanics Revision
Review problems
A parcel of mass 3kg is released from rest at the top of
a straight chute which is fixed at a 40o angle to the
horizontal. Given that the coefficient of friction
between the parcel and the chute is 0.2, and
neglecting any other resistances, calculate the
acceleration of the parcel as it slides down the chute.
Step 1 – Draw your diagram.
A parcel of mass 3kg is released from rest at the top of a straight chute which is fixed
at a 40o angle to the horizontal. Given that the coefficient of friction between the parcel
and the chute is 0.2, and neglecting any other resistances, calculate the acceleration of
the parcel as it slides down the chute.
F = ma
F = uR
Step 2 – Look at equations you might need
A parcel of mass 3kg is released from rest at the top of a straight chute which is fixed
at a 40o angle to the horizontal. Given that the coefficient of friction between the parcel
and the chute is 0.2, and neglecting any other resistances, calculate the acceleration of
the parcel as it slides down the chute.
F = m * a * sin(O)
F = 3 * g * sin(40)
F = 19.3N
Step 4 – Calculate with no friction
A parcel of mass 3kg is released from rest at the top of a straight chute which is fixed
at a 40o angle to the horizontal. Given that the coefficient of friction between the parcel
and the chute is 0.2, and neglecting any other resistances, calculate the acceleration of
the parcel as it slides down the chute.
R = m * g * cos(O)
R = 3 * 10 * cos(40)
R = 23N
Step 5 – Calculate the normal force
A parcel of mass 3kg is released from rest at the top of a straight chute which is fixed
at a 40o angle to the horizontal. Given that the coefficient of friction between the parcel
and the chute is 0.2, and neglecting any other resistances, calculate the acceleration of
the parcel as it slides down the chute.
F = uR
F = 0.2 * 23
F = 4.6
Step 6 – Calculate frictional force
A parcel of mass 3kg is released from rest at the top of a straight chute which is fixed
at a 40o angle to the horizontal. Given that the coefficient of friction between the parcel
and the chute is 0.2, and neglecting any other resistances, calculate the acceleration of
the parcel as it slides down the chute.
19.3 – 4.6 = 3 * a
a = 4.9 m/s2
Step 7 – Use Newton’s 2nd Law
A log, of mass 80kg, rests on horizontal ground.
When a force of magnitude 240N is applied to the log
in an upward direction that makes an angle of 20o
with the horizontal then the log is about to move.
Model the log as a particle and calculate the
coefficient of friction between the log and the ground.
Step 1 – Draw your diagram.
A log, of mass 80kg, rests on horizontal ground. When a force of magnitude 240N is
applied to the log in an upward direction that makes an angle of 20o with the
horizontal then the log is about to move. Model the log as a particle and calculate the
coefficient of friction between the log and the ground.
How to think about
this problem at first.
Step 1 – Draw your diagram.
A log, of mass 80kg, rests on horizontal ground. When a force of magnitude 240N is
applied to the log in an upward direction that makes an angle of 20o with the
horizontal then the log is about to move. Model the log as a particle and calculate the
coefficient of friction between the log and the ground.
Now model it as a
particle like the
problem asks.
Step 1 – Draw your diagram.
A log, of mass 80kg, rests on horizontal ground. When a force of magnitude 240N is
applied to the log in an upward direction that makes an angle of 20o with the
horizontal then the log is about to move. Model the log as a particle and calculate the
coefficient of friction between the log and the ground.
R = 800 – 240*sin(20)
R = 718N
Step 2 – Calculate normal force.
A log, of mass 80kg, rests on horizontal ground. When a force of magnitude 240N is
applied to the log in an upward direction that makes an angle of 20o with the
horizontal then the log is about to move. Model the log as a particle and calculate the
coefficient of friction between the log and the ground.
F = 240 * cos(20)
F = 225.5N
Step 3 – Calculate friction force.
A log, of mass 80kg, rests on horizontal ground. When a force of magnitude 240N is
applied to the log in an upward direction that makes an angle of 20o with the
horizontal then the log is about to move. Model the log as a particle and calculate the
coefficient of friction between the log and the ground.
F = uR
225.5 = u * 718
u = 0.314
Step 4 – Solve for coefficient of friction