1. Aim: How can we solve problems dealing with kinetic energy?
HW #9 due tomorrow
Hw #8
Answer Key
Do Now:
A force of 50 N is applied to an object which gives it a constant velocity of 10 m/s. At what rate is work being performed?
No Calculator
**1 minute**

2. Kinetic Energy
Energy of Motion
KE = ½mv2

3. 200 J of work are put into pushing a box across the floor.
How much kinetic energy has the object gained?
200 J
Work – energy relationship

4. 1. From the top of a high cliff, a ball is thrown horizontally with initial speed vo. Which of the following graphs best represents the ball's kinetic energy K as a function of time t ?
Look at the resultant K
Horizontal velocity is constant, therefore K is constant
Vertical velocity increases, therefore K increases
No Calculator
**1 minute**

5. 2. Which of the following quantities is scalar that is always positive or zero?
(A) Power
(B) Work
(C) Kinetic energy
(D) Linear momentum
(E) Angular momentum
Negative work is work done against friction
Power is work over time
Momentum is vector
No Calculator
**1 minute**

6. a. Calculate the force F necessary to keep the velocity constant.
3. A 10‑kilogram block is pushed along a rough horizontal surface by a constant horizontal force F as shown above. At time t = 0, the velocity v of the block is 6.0 meters per second in the same direction as the force. The coefficient of sliding friction is 0.2. Assume g = 10 meters per second squared.
a. Calculate the force F necessary to keep the velocity constant.
F = Ff
F = μN
F = μmg
F = (0.2)(10 kg)(10 m/s2)
F = 20 N
Calculator
**7.5 minutes**

7. The force is now changed to a larger constant value F'
The force is now changed to a larger constant value F'. The block accelerates so that its kinetic energy increases by 60 joules while it slides a distance of 4.0 meters.
b. Calculate the force F'.

8. c. Calculate the acceleration of the block.