Work, energy, and momentum problem solutions

Work, Energy, And Momentum

Work out the following problems. Be sure to show your work in detail. See the " uploaded file for examples of how the problems should be solved.

A freight elevator has a mass of 3,000 kg, including cargo. The elevator motor raises the load 50 m in 30 s. How much work is done by the motor? What is its power?

W= F*d

F=m*a

W=m*a*d

W= 3000kg *9.8m/s2*50m

W= 1,470,000J

P=W/t

P=1,470,000J/30s

P= 49,000W

What is the KE (in J) of a 2650 lb Honda Civic traveling at 100 mph?

KE=1/2mv2

Conversions from English to metric m=2650lb * 1kg/2.2 lb m=1204.55kg

100 mph * 1 hr/3600 sec * 1609.344 m/mi= 44.7 m/s

KE= 1/2 * 1204.55kg * (44.7m/s2)

KE= 1,203,399.7 J

A standard baseball weights 145 g. If it is thrown vertically with an initial velocity of 50 mph, what is its potential energy change at its highest point? How high does the baseball rise? Neglect air friction.

h=v2/2g

conversion from English to metric

mph *.44704 m/s

1 mph

22.352m/s h= (22.352 m/s) 2/2*9.8m/s2

h=25.49m

PE=Fd; F=ma

PE=m*a* d

PE=145g* 9.8m/s2* 25.49m

PE= 36,221.29J

4. Previously, we calculated the KE of a 2650 lb Honda Civic traveling at 100 mph. What is its momentum?

P=mv

P=2650lb * 1kg/2.2.lb * 100m/h * .44704m/s / 1 mph

P=20.32 kgm/s