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Mr. Chong is a washed up, desperate Tik Tok creator. He wants to film himself throwing a rock off of a high cliff. He wants it so that the rock will enter the water with a velocity of 12.2 m/s. How high of a cliff does he need to meet that velocity? Ignore Friction and Air Resistance. Hint: Does mass of the rock really matter?
Bonus: What will the velocity be halfway down the cliff?
TME_i+W_(ext)=TME_f
PE_i=KE_f
9.81*h=1/2(12.2)^2
h=7.59m
Bonus:
PE_i=PE_(half)+KE_(half)
9.81*7.586=9.81*7.586/2+1/2v^2
v_(half)=8.63
Mr. Chong, who is 70.0kg, rises from his chair 0.500 m to admit guilty for tax fraud in court. How much work did gravity do on Mr. Chong?
W_(ext)=(70*9.81)*0.5*cos180
W_(ext)=-343.35J->-343J
Define Inelastic and Elastic collisions.
Elastic: Energy is totally conserved. Work is 0.
Inelastic: Energy is transferred to another source (heat, sound). Work is not 0.
Draw an inelastic collision of two cars (explosive)
it better be something good
Your mother is so fat she has to use a wheel chair to travel. She weighs 287kg and has to go to the nearest 7-Eleven to get another Big Slurp. She travels 400 m at a constant speed on a level road. How much work did the wheelchair exert on your mother?
0 work! No change in velocity or height, so no change in energy!
What are the two things that need to be changed or altered to cause work?
Velocity and Height.
Bonus: Does direction matter for Work? Is work a vector quantity?
Mr. Chong is constantly dissatisfied with his therapist. On his most recent visit, he throws a heavy 10.4 kg picture frame with a velocity of 8 m/s at the 65kg therapist who is sitting still. Afterwards, the therapist flies back at 1.2 m/s. What is the final velocity of the picture frame?
Also, is the collision inelastic or elastic? If inelastic, find the work.
10.4*8+65*0=10.4*v_f+65*1.2
v_f=0.5m/s
1/2 10.4*8^2+0=1/2 10.4*0.5^2+1/2 65*1.2^2
Inelastic,
W_(ext)=48.1-332.8=284.7J
Mr. Chong is building a restaurant next to a Morgue (fresh ingredients). He drags a 30kg piece of lumber 20m across the parking lot with an angle of 25 degrees above the horizontal. If he exerts 180J of work on the lumber, how much force did he apply?
W_(ext)=Fdcos\theta
180=F20cos25
F=9.9N
If I triple the speed of a bullet, how will that affect the kinetic energy?
Multiply by 9.