Incline Problem (Physics)

Question

1. A diver who has a mass of 70.0 kg stands on a 10.0-meter diving platform.

a) Potential Energy of the diver

b) Potential energy of the diver 4.00 m from the water

c) What is his kinetic energy 4.00 m from the water

2. How much work is performed by pulling a machine weighing 7000 N up an incline 120 m long and 16.0 m high?

Answer 1

Standing on diving board (not moving)

1. all energy is potential energy
2. Kinetic energy is 0 because we are not moving

PE = mgh

m = 70.0kg

h = 10.0m

g = 9.8 m/s^2

PE = (70.0)(9.8)(10.0) = 6860 J

KE = 0 J

**The total energy of the whole system is PE + KE

Total Energy = 6860 J

At all points on this dive, PE + KE = 6860 J **

At 4.00m away from the water

1. some energy is PE
2. some energy is KE

PE = mgh

m = 70.0kg

g = 9.8 m/s^2

h = 4.00m height above water

PE = (70.0)(9.8)(4.00) = 2744 J

To find KE at 4.00m above the water, use the total energy

PE + KE = total

2744 + KE = 6860

KE at 4.00m above water = 4116 J

#2 Work = Force * distance

when the force and distance are pointing in the same direction (x or y)

If we are pulling an object up an incline, what we are fighting is the weight of the object. The weight of the object points straight down (think of your free body diagrams).

The work done by pulling the object up the ramp is only generated by how far up the object moves to counteract the force of weight going down. The length of the ramp does not matter —> just the height. Assuming we are pulling with a constant speed (which your teacher needed to specify), we must do enough work to exactly counteract the force of gravity pulling down on the machine.

Work = F* d

F = weight of machine = 7000 N

d = height of incline = 16.0m

Work = (7000)(16.0) = 112,000 J