Expt Activity 14 A popular toy is part of a hollow rubber sphere that pops when

Question

Expt Activity 14 A popular toy is part of a hollow rubber sphere that pops when inverted and dropped. It is often called a popper: Cock the supplied popper a few times. You may find you need to curl the edges down a bit to get it to stay cocked Uncocked You will be using two Force Sensors in parallel to measure the force needed to cock the popper. The program that reads the two Force Sensors and displays their sum is named ForceSensorsDoubled. For more details see the Force Sensor manual at: Cocked You will use the supplied "hook and piece of Plexiglas with a hole in it as shown. Be sure to center the popper on the hole in the Plexiglas, or the popper can get pulled through the hole when it is cocked A Use the doubled Force Sensors to estimate the force needed to cock the popper. Estimate the total work you need to do to cock it. Where did the energy go? Force Sens Pull the Plexiglass to the right

Explanation / Answer

A. A normal popper takes a force of about F = 10 N to be cocked

now, the distance moved by the edges of the popper while cocking is about d = 3 cm

then average work doine on the popper, W = F*d = 10*3/100 = 0.3 J

this energy is being used to cock the popper ( i.e) to change its shape, just like energy stored in a spring when it is streched

B. now, mass of a popperf, m = 50 g

initial drop height, h = 1 m

initial PE = mgh = 0.05*9.81*1 = 0.4905 J

stored energy = 0.3 J

so when it uncocks, total eneregy = 0.4905 + 0.3 = 0.7905 J

so the height to whioch it flies = H

mgH = 0.7905 = 0.05*9.81*H

H = 1.611 m

so the poppper should fly to a height of about 1.6 m ewhen dropped from a height of 1 m

C. for the popper to be the system

when it is cocked, work is done on the popper to deform its shape, and hence it stored that work in the form of elastic potential energy

D. when dropped to a floor, the initial potential energy due to its height is transferred to the kinetic energy as it reaches the floor

this extra energy is transformed into some elastic potential energy , which transforms the shape of the popper moire, to destabilise its cocked equilibrium and hence uncocks it too

this KE with the stored elastic potential energy tis conv erted back to the potential energy of the popper as it flies back to a height greaster than the height it was dropped from

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