Check for Understanding
A sling shot is used to shoot a water balloon (balloon mass = 2kg) at a target 15m away.
If the spring constant k for the sling shot tubing is equal to 250N/m, find the following:
1.) PEs when the tubing is stretched .75m
2.) The velocity of the balloon as it leaves the sling shot using energy conservation.
Nov 30­11:38 AM
1
Dec 1­9:26 AM
2
A toy gun uses a spring to project a 0.008kg rubber sphere horizontally. The spring constant is 7.0N/m, the barrel of the gun is 0.12m long, and a constant frictional force of 0.04N exists between the barrel and the projectile (rubber sphere). With what speed does the projectile leave the barrel if the spring is compressed 0.06m for this launch?
a.) Find PEs of the spring prior to launch:
b.) Find the energy lost to friction down the barrel:
c.) Find the remaining energy that is transformed into the KE of the projectile:
Jan 13­7:31 AM
3
1. A spring­loaded toy dart gun is used to shoot a dart straight up in the air, and the dart reaches a maximum height of 24 m. The same dart is shot straight up a second time from the same gun, but this time the spring is compressed only half as far as before firing. How far up does the dart go this time, neglecting friction and assuming an ideal spring?
Jan 13­8:02 AM
4
2. When a 50 kg person is hangs from a 20 m bungee cord it stretches to a length of 32 m.
﴾a﴿ Find the spring constant of the bungee cord, assuming it obeys Hooke's law.
﴾b﴿ How much work is required to stretch the cord by this much?
﴾c﴿ How heavy a person is required to make the cord stretch twice as much?
﴾d﴿ How much additional work is required to make the cord stretch twice as much?
Jan 13­8:07 AM
5
4. A ski lift carries a 75kg skier at 3.0m/s for 1.5 minutes along a cable that is inclined at an angle of 40o above the horizontal. a.) How much work is done by the ski lift?
b.) How much power is expended by the ski lift?
Jan 13­7:28 AM
6
5. An electric motor lifts an elevator at a constant speed of 54 km/h. The engine must exert a force of 9kN in order to balance the weight of the elevator and the friction in the elevator cable. What power does the motor produce in kW?
Jan 13­7:29 AM
7
Jan 13­8:36 AM
8
Nov 30­11:34 AM
9