What do we want to do today?! Tuesday: 29-1-1440 A bit of housekeeping Conclude chapter-7 (possibly) introduce chapter-8 Prof. Zain Yamani Office: 15-3100/ 3102; Phone: 860-4363; Mobile: 0504608515 E-Mail: zhyamani@kfupm.edu.sa; HP: http://faculty.kfupm.edu.sa/phys/zhyamani

A bit of housekeeping Attendance If you come late, please make me aware during the (end of) the same lecture.

A bit of housekeeping Mathematica is presumably available in: Building 4/104 Building 7/ 137 Building 66/230 Library

A bit of housekeeping Raise your hand if you are committed to attending a Help Session tomorrow (Wednesday) at 5.45 – 7.00 p.m.

Challenge: add friction!!  A racing car speeds on a circular (radius: R) track that is banked at angle (q) with the horizontal. The car mass is (m) and the coefficient of static friction between car and track is m. Draw a schematic of the problem. Calculate the maximum speed that the car can run without skidding off. In what ways can this “maximum” speed be improved?

Chapter-7: Energy Kinetic Energy Work Work done by Weight (gravity) Work done by Spring Power

What did we learn about last lecture?

A rope exerts a force F on on a 20 A rope exerts a force F on on a 20.0 kg crate in lifting it vertically upward above the floor. The crate starts from rest and accelerates upward at 5.00 m/s2. How much work was done by the force F in raising the crate 4.00 m above the floor? A) 1.18 kJ B) 1.98 kJ C) 2.50 kJ D) 1.71 kJ E) 0.704 kJ 101-2

What if the work is done by a spring? The relaxed: non-stretched/ non-extended, non- compressed state. The spring force is a (linear) “restoring” force. Spring (or Force) constant: k F = - k d What does big “k” mean? SI units for “k”?

What is the relation between their speeds at the instant of launch? Two balls are launched from the same spring-loaded cannon with the spring compressed the same distance each time. Ball A has a 40 kg mass and ball B has a 60 kg mass. What is the relation between their speeds at the instant of launch? 141-2

What is the relation between their speeds at the instant of launch? Two balls are launched from the same spring-loaded cannon with the spring compressed the same distance each time. Ball A has a 40 kg mass and ball B has a 60 kg mass. What is the relation between their speeds at the instant of launch? 141-2

Work done by a general variable force (omitted)

Average and Instantaneous Power P, units of P Pavg Pinstanaeous The horsepower = 746 watt

The tension force is parallel to the incline. A constant tension force is used to pull a 50.0 kg box up a frictionless plane inclined at 30.0° relative to the horizontal. The tension force is parallel to the incline. The box is moved a distance of 30.0 m along the incline with a constant speed of 1.00 m/s. At what rate is work done by the tension force? A) 245 W B) 49.3 W C) 98.0 W D) 292 W E) 495 W 101-2

A 0.50 kg object, moving along the x-axis, experiences the force shown in the Figure. The object’s velocity at x = 0.0 m is v = 2.0 m/s, and at x = 4.0 m is v = 8.0 m/s. What is Fmax? A) 5.0 N B) 7.2 N C) 9.7 N D) 3.2 N E) 1.8 N 101-2