PHYSICS EXAM TOMORROW...I need help with energy please!!?

Question

I have answers but don’t know how to get them. Thanks!
1) The hill is 8 m tall. How much work is needed to move a 150-kg sofa to the hilltop? (Answer: 1 * 10^4 Joules)
2) 300 N force is used to push a 145-kg mass 30 m horizontally in 3 seconds. Find work done on the mass (answer:9.00 kJ) & the power developed (Ans: 3.00 kW)
3) Al & his bike have a combined mass of 45 kg. Al rides his bike 1.8 km in 10 min at constant velocity. What’s Al’s kinetic energy? (Ans: 203 Joules)
4) A train has mass of 2.50 * 10^4kg. Its powered across a level track by an engine that made a thrust of 5 * 10^5 N for 509 meters. Find…
a. work done on the train (ans: 2.55 * 10^8 J)
b. change in Kinetic Energy (same as a)
c. final KE of train if it started from rest (same as b)
d. final speed of train if there was no friction: (ans: 143 m/s)
5) Al’s mass =28 kg. He climbs the 4.8 m slide ladder & reaches velocity of 3.2 m/s at bottom of the slide. How much work did friction do on Al? (Ans: -1.2 * 10^³ J

Answer 1

OK
1. The work done represents the change in total energy (kinetic + potential). The potential energy of a mass in a gravitational acceleration is
Ep = mgh where m is mass, g is gravitational acceleration, and h is height. So the change in potential energy of the 150 kg sofa is
W = mgh = 140*9.8*8 = 11,760 J

2.
Work is force applied through a distance or
W = fd so the work done is
W = 300*30 = 9,000 J Power is the rate at which work is done
P = W/t so
P = 9,000J/3 s = 3,000 Watts.

Now **you** do the rest of them because I'm not gonna be there to take your test for you. You have to learn this stuff. I already learned it 40+ years ago ☺

Doug

Answer 2

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