Work Kinetic Energy A force F= 10N pushes a box across a frictionless floor for a distance Ax= 5m. the speed of the box is v before the push, and v2 after the push F △X Physics 121: Lecture 12, Pg 11
Physics 121: Lecture 12, Pg 11 Work & Kinetic Energy: A force F = 10N pushes a box across a frictionless floor for a distance x = 5m. The speed of the box is v1 before the push, and v2 after the push. x F v1 v2 i m
Work Kinetic Energy Since the force f is constant acceleration a will be constant. We have shown that for constant a: 2a(X2×X1)=2a△X multiply by 'l,m /2mV2-12mV12=ma△X But F= ma 2mv2-12m F△x F m △X Physics 121: Lecture 12, Pg 12
Physics 121: Lecture 12, Pg 12 Work & Kinetic Energy... Since the force F is constant, acceleration a will be constant. We have shown that for constant a: v2 2 - v1 2 = 2a(x2 -x1 ) = 2ax. multiply by 1 /2m: 1 /2mv2 2 - 1 /2mv1 2 = ma x But F = ma 1 /2mv2 2 - 1 /2mv1 2 = Fx x F v1 v2 a i m
Work Kinetic Energy. ■■ So we find that 1l2mv22-12mV, =FAX WE Define Kinetic Energy KE: KE=1/2mv KE2-KE,=WE WE=AKE Work kinetic-energy theorem) F △X Physics 121: Lecture 12, Pg 13
Physics 121: Lecture 12, Pg 13 Work & Kinetic Energy... So we find that 1 /2mv2 2 - 1 /2mv1 2 = Fx = WF Define Kinetic Energy KE: KE = 1 /2mv2 KE2 - KE1 = WF WF = KE (Work kinetic-energy theorem) x F v1 v2 a i m
Work Kinetic-Energy Theorem INet Work done on object] Change in kinetic energy of object W=△K K-K mv mV Physics 121: Lecture 12, Pg 14
Physics 121: Lecture 12, Pg 14 Work Kinetic-Energy Theorem: {Net Work done on object} = {change in kinetic energy of object} Wnet = K = K2 − K1 2 1 2 2 mv 2 1 mv 2 1 = −
Lecture 12 2 Kinetic Energy To practice your pitching you use two baseballs. The first time you throw a slow curve and clock the speed at 50 mph(-25 m/s). The second time you go with high heat and the radar gun clocks the pitch at 100 mph. What is the ratio of the kinetic energy of the fast ball versus the curve ball (a)(b)1/2(c)1(0)2(e)4 8 Physics 121: Lecture 12, Pg 15
Physics 121: Lecture 12, Pg 15 Lecture 12, ACT 2 Kinetic Energy To practice your pitching you use two baseballs. The first time you throw a slow curve and clock the speed at 50 mph (~25 m/s). The second time you go with high heat and the radar gun clocks the pitch at 100 mph. What is the ratio of the kinetic energy of the fast ball versus the curve ball ? (a) 1/4 (b) 1/2 (c) 1 (d) 2 (e) 4