If a boy (m = 50kg) at rest on skates is pushed by another boy who exerts a force of 200 n on him and if the first boy's final velocity is 8 m/s, what was the contact time?

An engine undergoes a cycle as shown in the diagram. during a complete cycle the work done by the gas is 28.5×103 j and the energy transferred thermally out is 99.4×103 j. there are 1.5×1024 gas molecules and they have three active degrees of freedom. 6. (6 pts) during which process(es) is energy transferred thermally into the gas? a. 1→2 b. 2→3 c. 4→1 d. 1→2 and 4→1 e. none of the above

The bar of prob. 5/82 is repeated here. the ends of the 0.4-m bar remain in contact with their re- spective support surfaces. end b has a velocity of 0.5 m/s and an acceleration of 0.3 m/s2 in the di- rections shown. determine the angular accelera- tion of the bar and the acceleration of end a.

List and describe three ways that humans can change ecosystems and three ways that humans can protect ecosystems.