Answer:
When have passed 3.9[s], since James threw the ball.
Explanation:
First, we analyze the ball thrown by James and we will find the final height and velocity by the time two seconds have passed.
We'll use the kinematics equations to find these two unknowns.
![y=y_{0} +v_{0} *t+\frac{1}{2} *g*t^{2} \\where:\\y= elevation [m]\\y_{0}=initial height [m]\\v_{0}= initial velocity [m/s] =41.67[m/s]\\t = time passed [s]\\g= gravity [m/s^2]=9.81[m/s^2]\\Now replacing:\\y=0+41.67 *(2)-\frac{1}{2} *(9.81)*(2)^{2} \\\\y=63.72[m]\\](https://tex.z-dn.net/?f=y%3Dy_%7B0%7D%20%2Bv_%7B0%7D%20%2At%2B%5Cfrac%7B1%7D%7B2%7D%20%2Ag%2At%5E%7B2%7D%20%5C%5Cwhere%3A%5C%5Cy%3D%20elevation%20%5Bm%5D%5C%5Cy_%7B0%7D%3Dinitial%20height%20%5Bm%5D%5C%5Cv_%7B0%7D%3D%20initial%20velocity%20%5Bm%2Fs%5D%20%3D41.67%5Bm%2Fs%5D%5C%5Ct%20%3D%20time%20passed%20%5Bs%5D%5C%5Cg%3D%20gravity%20%5Bm%2Fs%5E2%5D%3D9.81%5Bm%2Fs%5E2%5D%5C%5CNow%20replacing%3A%5C%5Cy%3D0%2B41.67%20%2A%282%29-%5Cfrac%7B1%7D%7B2%7D%20%2A%289.81%29%2A%282%29%5E%7B2%7D%20%5C%5C%5C%5Cy%3D63.72%5Bm%5D%5C%5C)
Note: The sign for the gravity is minus because it is acting against the movement.
Now we can find the velocity after 2 seconds.
![v_{f} =v_{o} +g*t\\replacing:\\v_{f} =41.67-(9.81)*(2)\\\\v_{f}=22.05[m/s]](https://tex.z-dn.net/?f=v_%7Bf%7D%20%3Dv_%7Bo%7D%20%2Bg%2At%5C%5Creplacing%3A%5C%5Cv_%7Bf%7D%20%3D41.67-%289.81%29%2A%282%29%5C%5C%5C%5Cv_%7Bf%7D%3D22.05%5Bm%2Fs%5D)
Note: The sign for the gravity is minus because it is acting against the movement.
Now we can take these values calculated as initial values, taking into account that two seconds have already passed. In this way, we can find the time, through the equations of kinematics.
As we can see the equation is based on Time (t).
Now we can establish with the conditions of the ball launched by David a new equation for y (elevation) in function of t, then we match these equations and find time t
![y=y_{o} +v_{o} *t+\frac{1}{2} *g*t^{2} \\where:\\v_{o} =55.56[m/s] = initial velocity\\y_{o} =0[m]\\now replacing\\63.72 +22.05 *t-(4.905)*t^{2} =0 +55.56 *t-(4.905)*t^{2} \\63.72 +22.05 *t =0 +55.56 *t\\63.72 = 33.51*t\\t=1.9[s]](https://tex.z-dn.net/?f=y%3Dy_%7Bo%7D%20%2Bv_%7Bo%7D%20%2At%2B%5Cfrac%7B1%7D%7B2%7D%20%2Ag%2At%5E%7B2%7D%20%5C%5Cwhere%3A%5C%5Cv_%7Bo%7D%20%3D55.56%5Bm%2Fs%5D%20%3D%20initial%20velocity%5C%5Cy_%7Bo%7D%20%3D0%5Bm%5D%5C%5Cnow%20replacing%5C%5C63.72%20%2B22.05%20%2At-%284.905%29%2At%5E%7B2%7D%20%3D0%20%2B55.56%20%2At-%284.905%29%2At%5E%7B2%7D%20%5C%5C63.72%20%2B22.05%20%2At%20%3D0%20%2B55.56%20%2At%5C%5C63.72%20%3D%2033.51%2At%5C%5Ct%3D1.9%5Bs%5D)
Then the time when both balls are going to be the same height will be when 2 [s] plus 1.9 [s] have passed after David throws the ball.
Time = 2 + 1.9 = 3.9[s]
C. It transfer energy as heat to the surrounding air. This answer is incorrectly
When an unbalanced force acts on an object the change in the object state of rest or motion depends on the size and direction of the force.
If a body is at state of rest or motion, when an unbalanced external force acts on it, its starts moving in the direction of force and magnitude of its velocity or acceleration depends on the magnitude of force applied.
Answer:
both the same
Explanation:
When a ball is thrown vertically upwards, it experiences that same acceleration due to gravity as an object thrown directly downwards.
This means that if we ignore the effects of air resistance, and the two balls have the same initial speed, they are expected both expected to hit the ground at the same speed as a result of the principle of conservation of energy.
Answer:
E. two times the original diameter
Explanation:
Resistance of a wire is:
R = ρ L/A
where ρ is the resistivity of the material, L is the length, and A is the cross-sectional area.
For a round wire with diameter d:
R = ρ L / (¼ π d²)
The two wires must have the same resistance, so:
ρ₁ L₁ / (¼ π d₁²) = ρ₂ L₂ / (¼ π d₂²)
The wires are made of the same material, so ρ₁ = ρ₂:
L₁ / (¼ π d₁²) = L₂ / (¼ π d₂²)
The new length is four times the old, so 4 L₁ = L₂:
L₁ / (¼ π d₁²) = 4 L₁ / (¼ π d₂²)
1 / (¼ π d₁²) = 4 / (¼ π d₂²)
Solving:
1 / (d₁²) = 4 / (d₂²)
(d₂²) / (d₁²) = 4
(d₂ / d₁)² = 4
d₂ / d₁ = 2
So the new wire must have a diameter twice as large as the old wire.
