Lets do the sum of the forces about the elbow joint.
Fm = Force of Muscle; Fe = Force Elbow; Fb = Force Ball
Sum Force about Joint = (-2.5)Fm + 12.5Fe + 30Fb = 0
(-2.5)Fm + 12.5(2.8) + 30(6.9) = 0
Fm = 96.8kg
Fm = 96.8 * 9.8 = 948.6N
Do you understand why the -2.5 is negative?
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Because I put the origin at the joint. So when you go left it is negative and when you go right it is positive. </span>
This is a problem of conservation of momentum
Momentum before throwing the rock: m*V = 96.0 kg * 0.480 m/s = 46.08 N*s
A) man throws the rock forward
=>
rock:
m1 = 0.310 kg
V1 = 14.5 m/s, in the same direction of the sled with the man
sled and man:
m2 = 96 kg - 0.310 kg = 95.69 kg
v2 = ?
Conservation of momentum:
momentum before throw = momentum after throw
46.08N*s = 0.310kg*14.5m/s + 95.69kg*v2
=> v2 = [46.08 N*s - 0.310*14.5N*s ] / 95.69 kg = 0.434 m/s
B) man throws the rock backward
this changes the sign of the velocity, v2 = -14.5 m/s
46.08N*s = - 0.310kg*14.5m/s + 95.69kg*v2
v2 = [46.08 N*s + 0.310*14.5 N*s] / 95.69 k = 0.529 m/s
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Answer: Something that's vibrating, and you also need medium for those vibrations to start in.
I hope this helped!
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- Zack Slocum
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I believe the answer is the mass of the object and the speed at which it is moving.