Transcript Because energy is a scalar, it is often easier to

Because energy is a scalar, it is often easier to analyze motion
using conservation as energy, rather than kinematics or force
analysis. This way, trig is avoided.
A 3 kg projectile is fired straight off of a 100 m high cliff at 50 m/s.
Find the velocity when it hits the ground using conservation of
energy.
A 1 kg ball is hit at 30° and goes 10 meters high in the air. Find the
speed at the top using the conservation of energy approach.
Forces do work
• When forces do work, energy is transferred.
• Sometime all the work goes into speeding an object up;
W = ΔKE
• Example #1: 5000 Joules of work are done to
speed up a 1000 kg object. Find its new speed,
assuming no friction is present.
• The car is let go on a road with friction. Find the work
done by friction to stop the object.
• Assuming the coefficient of friction is 0.2 find the
“stopping distance” that is needed for friction to bring the
car to rest.
• Is the work done by friction on the car + or - ?