A steel ball has a mass of 4 kg and rolls along a smooth level surface at 62 m/s.(adsbygoogle = window.adsbygoogle || []).push({});

a) Find its kinetic energy ( i found this.. )

b) At first, the ball was at rest on the surface. A constant force acted on it through a distance of 22 m to give it the speed of 62 m/s. What was the magnitude of the force?

so heres my thought process:

.5 mv^2 + mgh = .5mv^2 + mgh

0 = .5mv^2+mgh

-.5mv^2=mgh

mg=- .5mv^2/h

mg= - .5 x 4 x 62^2/22

mg= -350 N

is the above method correct?

Q2) In the 1950's, an experimental train that had a mass of 2.50x10^4 was powered across a level track by a jet engine that produced a thrust of 5x10^5 N for adistance of 509 m.

a) Find the work done on the train. ( found this to be 2.545E8)

b) Find the change in kinetic energy. ( 2.545E8)

c) Find the final kinetic energy of the train if it started from rest. ( how do i find this?? .5 mv^2 wont wrk since i dunno waht the velocity is )

d) find the final speed of the train if there were no friction ( how do i find this?? )

thanks much

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# Homework Help: Energy prob

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