Work
A work is done by the...
Force
What determines the sign (+ or -) of a force?
The direction of the motion
T/F
Friction is proportional to the normal
force
True
What causes a change in energy?
What is the unit of Work?
Joules (J)
How do you calculate the Work?
by exerting a constant force, F is the
product of the displacement and the
component of F along r
W = F cos(angle) (r)
An egg is free-falling from a nest in a tree. Neglect air resistance. Diagram the forces acting on the egg as it is falling.
mg is -
Fs is positive when a spring is...
compressed
What is Kinetic Energy?
Is the energy of a particle due to its motion
Can the work be zero?
Yes, when it is perpendicular to the displacement
A 10 kg weight is suspended in the air by a strong cable. How much work is done, per unit time, in suspending the weight?
There is no work in the system
A girl is suspended motionless from a bar which hangs from the ceiling by two ropes. Diagram the forces acting on the girl.
2 Tension is +
mg is -
A 3.00 kg block starts from the rest at the top of a 30.0o incline and slides a distance of 2.00 m down the incline in 1.50 s. The acceleration of the block is 1.78m/s^2
Find the coefficient of kinetic friction between block and plane.
uk = 0.368
What is the Kinetic Energy of a 150 kg object that is moving with a speed of 15 m/s?
KE = 16875J
What is the resistance to the motion?
Friction force
A crate is moved across a frictionless floor by a rope that is inclined 30 degrees above the horizontal. The tension in the rope is 50 N. How much work is done in moving the crate 10 meters?
W = F*r*cosθ = (50)(10)(cos 30) = 433 J
A car is coasting to the right and slowing down. Diagram the forces acting upon the car.
Friction is -
Normal is +
mg is -
A 3.00 kg block starts from the rest at the top of a 30.0o incline and slides a distance of 2.00 m down the incline in 1.50 s. The acceleration of the block is 1.78m/s^2
Find the friction force on the block.
fk = 9.37N
An object has a kinetic energy of 88 J and a mass of 45 kg , how fast is the object moving?
v = 1.98m/s
If work is done on a system only
causes a change in its...
Speed
*System = object in motion