Answer:
1.78 D
Explanation:
v = 25 cm
u = 45 cm
use lens equation
1 / f = 1 / v - 1 / u
1 / f = 1 / 25 - 1 / 45
1 / f = (45 - 25) / 25 x 45
1 / f = 20 / 25 x 45
Power, P = 100 / f (m)
P = 2000 / 25 x 45 = 1.78 D
Thus, the power of lens is 1.78 D.
Answer:
Well they could do an experiment
Explanation:
Not do sure, but hope this helps.. chow
The efficiency of the appliance is 0.62 (62%)
Explanation:
The relationship between the power of the appliance and the energy used by it is
where
P is the power
E is the energy transferred in input
t is the time elapsed
For this appliance,
P = 7 W
So, in t = 42 s, the energy transferred in input is
We are told that the useful energy in output however is
Therefore, the efficiency of the appliance is
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Answer:
F = 62.4 N
Explanation:
We must solve this problem in two parts, the first with energy to find the speed with which it reaches the grass and with impulse to determine the strength in the grass
Let's look for the speed of arrival to the grass, write the energy in two points
Initial
Em₀ = U = m g h
Point 2, just by touching the grass
Em₂ = K = ½ m v²
Em₀ = Em₂
m g h = ½ m v²
v = √ 2gh
v = √( 2 9.8 2.8)
v = 7.4 m/s
Let's calculate the momentum until it stops
I = F t = m vf -m v₀
I = 0-0.15 (-7.4)
I = 1.11 N s
We must find the time during which the apple stops, let's use kinematics to find the average acceleration
= v = 7.4 m/s
² = v₀² + 2 a y
0 = v₀² + 2 a y
a = v₀² / 2y
a = 7.4²/2 0.066
a = 414.85 m / s²
Now let's look for the time to stop with this acceleration
= v₀ + at
0 = v₀ + at
t = v₀ / a
t = 7.4 / 414.85
t = 0.0178 s
Let's calculate with the momentum
I = F t
F = I / t
F = 1.11 / 0.0178
F = 62.4 N