WHITE BOARD TIME !!

CONSERVE ENERGY

ET = PEG + KE + PES

When comparing the energy at two different positions on a system, the total energy at one position, A, will be equal to the total energy at another position, B, provided no net work is done on the system.The SUM of all of the types of mechanical energy present in the system should stay the same..

The total mechanical energy of a system can be found by the SUM of each type of mechanical energy present in the system.

A 60 kg swimmer at a water park enters a pool using a 2 m high slide.

1.Find the velocity of the swimmer at point B, h= 0m.

2.Determine the height of the slide when the swimmer is moving 5 m/s.

3.Determine the speed of the swimmer when the height of the slide is 0.8 m.

A

B

A 55 kg skateboarder enters a ramp moving horizontally with a speed of 6.5 m/s and leaves the ramp moving vertically with a speed of 4.1 m/s. 1.Find the height of the ramp

2.Find the maximum height reached by the skate boarder once he leaves the ramp.

3.Determine the speed of the skateboarder when the height of the slide is 0.8 m.

AB

C

Tarzan running at 8 m/s grabs on to a vertically hanging vine and swings up.

1.Use the work energy principle to determine how high he will swing up. Air resistance is negligible.

2.If the vine is 17 m long, will Tarzan make it across the 10 m wide ravine?

3. What is ?

A 4 kg bowling ball is drop from rest at a height of 1 m. There is an unstretched spring below. Once the bowling ball touches the spring, the bowling ball is slowed down to rest, and completely compresses the spring. The spring constant is 490 N/m. Write down the given information to solve the problem on the next slide.

V = 0 m/s

dy (m)

0.0

0.5

A B C D E

0.6

0.30.4

0.10.2

0.91.0

0.70.8

V = 0 m/s

dy (m)

0.0

0.5

A B C D E

0.6

0.30.4

0.10.2

0.91.0

0.70.8

At position D, the spring is compressed a ∆L of 0.2 m. The 4 kg bowling ball is up at height of 0.2 meters above the reference height. Find the velocity of the ball at position D.

A 2000N/m spring is compressed a distance of 30 cm against a wall with a 0.75 kg block ready to be released off the spring. The block is released and it slides along a frictionless surface.

a. Calculate the elastic potential energy stored in the spring.b. Calculate the speed of the block when it is released.c. The block then glides onto a rough surface where the coefficient of kinetic friction measured between the block and the surface is 0.25. How far does the block slide before it comes to a rest?