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____ [38]
3 years ago
15

Now let’s apply the work–energy theorem to a more complex, multistep problem. In a pile driver, a steel hammerhead with mass 200

kg is lifted 3.00 m above the top of a vertical I-beam that is to be driven into the ground (Figure 1) . The hammer is then dropped, driving the I-beam 7.40 cm farther into the ground. The vertical rails that guide the hammerhead exert a constant 60.0 N friction force on it. Use the work–energy theorem to find
(a) the speed of the hammerhead just as it hits the I-beam and
(b) the average force the hammerhead exerts on the I-beam.
Physics
1 answer:
andrew11 [14]3 years ago
6 0

Answer:

a) v = 7.67

b) n = 81562 N

Explanation:

Given:-

- The mass of hammer-head, m = 200 kg

- The height at from which hammer head drops, s12 = 3.00 m

- The amount of distance the I-beam is hammered, s23 = 7.40 cm

- The resistive force by contact of hammer-head and I-beam, F = 60.0 N

Find:-

(a) the speed of the hammerhead just as it hits the I-beam and

(b) the average force the hammerhead exerts on the I-beam.

Solution:-

- We will consider the hammer head as our system and apply the conservation of energy principle because during the journey of hammer-head up till just before it hits the I-beam there are no external forces acting on the system:

                                   ΔK.E = ΔP.E

                                  K_2 - K_1 = P_1- P_2

Where,  K_2: Kinetic energy of hammer head as it hits the I-beam

             K_1: Initial kinetic energy of hammer head ( = 0 ) ... rest

             P_2: Gravitational potential energy of hammer head as it hits the I-beam. (Datum = 0)

             P_1: Initial gravitational potential energy of hammer head      

- The expression simplifies to:

                                K_2 = P_1

Where,                     0.5*m*v2^2 = m*g*s12

                                v2 = √(2*g*s12) = √(2*9.81*3)

                                v2 = 7.67 m/s

- For the complete journey we see that there are fictitious force due to contact between hammer-head and I-beam the system is no longer conserved. All the kinetic energy is used to drive the I-beam down by distance s23. We will apply work energy principle on the system:

                               Wnet = ( P_3 - P_1 ) + W_friction

                               Wnet = m*g*s13 + F*s23

                               n*s23 = m*g*s13 + F*s23

Where,    n: average force the hammerhead exerts on the I-beam.

               s13 = s12 + s23

Hence,

                             n = m*g*( s12/s23 + 1) + F

                             n = 200*9.81*(3/0.074 + 1) + 60

                             n = 81562 N

                               

                                                   

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Answer:

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Explanation:

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5 0
3 years ago
98. In Fig. 24-71, a metal sphere
yarga [219]

Answer:

(a) The potential difference between the spheres is 750 kVA

(b) The charge on the smaller sphere is 6.\overline 6 μC

(c) The charge on the smaller sphere, Q₁ = 13.\overline 3 μC

Explanation:

(a) The given parameters are;

The charge on the inner sphere, q = 5.00 μC

The radius of the inner sphere, r = 3.00 cm = 0.03 m

The charge on the larger sphere, Q = 15.0 μμC

The radius of the larger sphere, R = 6.00 cm = 0.06 m

The potential difference between two concentric spheres is given according to the following equation;

V_r - V_R = k \times q \times \left ( \dfrac{1}{r} - \dfrac{1}{R} \right)

Where;

R = The radius of the larger sphere = 0.06 m

r = The radius of the inner sphere = 0.03 m

q = The charge of the inner sphere = 5.00 × 10⁻⁶ C

Q = The charge of the outer sphere = 15.00 × 10⁻⁶ C

k = 9 × 10⁹ N·m²/C²

Therefore, by plugging in the value of the variables, we have;

V_r - V_R = 9 \times 10^9  \times 5.00 \times 10^{-6} \times \left ( \dfrac{1}{0.03} - \dfrac{1}{0.06} \right) = 750,000

The potential difference between the spheres, V_r - V_R = 750,000 N·m/C = 750 kVA

(b) When the spheres are connected with a wire, the charge, 'q', on the smaller sphere will be added to the charge, 'Q', on the larger sphere which as follows;

Q_f = Q + q = (5 + 15) × 10⁻⁶ C = 20 × 10⁻⁶ C

Q_f = 20 × 10⁻⁶ C

From which we have;

Q₁/Q₂ = R/r

Where;

Q₁ = The new charge on the on the larger sphere

Q₂ = The new charge on the on the smaller sphere

Q_f = 20 × 10⁻⁶ C = Q₁ + Q₂

∴ Q₁ = 20 × 10⁻⁶ C - Q₂ = 20 μC - Q₂

∴ (20 μC - Q₂)/Q₂ = 0.06/(0.03) = 2

20 μC - Q₂ = 2·Q₂

20 μC = 3·Q₂

Q₂ = 20 μC/3

The charge on the smaller sphere, Q₂ = 20 μC/3 = 6.\overline 6 μC

(c) Q₁ = 20 μC - Q₂ = 20 μC - 20 μC/3 = 40 μC/3

The charge on the smaller sphere, Q₁ = 40 μC/3 = 13.\overline 3 μC.

5 0
3 years ago
Someone drops a 50 − g pebble off of a docked cruise ship, 70.0 m from the water line. A person on a dock 3.0 m from the water l
alexira [117]

Answer:

a) The work done on the pebble is 32.9 J.

b) The change in the gravitational potential energy is -32.9 J.

c) When the pebble is dropped, the potential energy is 34.3 J.

d) When the pebble reaches the net, the potential energy is 1.47 J.

e) If the potential energy is 30.0 J at water level, it will be 31.47 J at the net and 64.3 J at 70.0 m.

Explanation:

a) The work done by the gravity force can be calculated using the following equation:

W = F · Δy

Where:

W = work

F = gravity force

Δy = vertical displacement (final height - initial height)

The gravity force can be calculated as:

F = m · g

Where:

F = gravity force

m = mass

g = acceleration due to gravity (-9.81 m/s² considering the upward direction as positive).

Then, the work done on the pebble by the gravity force will be:

W = m · g · (hf - hi) (hf = final height, hi = initial height)

W = 0.050 kg · (-9.81 m/s²) · (3.0 m - 70.0 m)

W = 32.9 J

The work done on the pebble is 32.9 J.

(Notice that the work is positive. That means that the force that does the work is in the same direction as the movement).

b) The potential energy (EP) can be calculated as follows:

EP = m · g · h (h = height)

The change in the gravitational potential energy is calculated as the difference of the potential energy between the two positions:

ΔEP = EPf - EPi

Where:

ΔEP = change in the gravitational potential energy.

EPf = final potential energy.

EPi = initial potential energy.

Then:

ΔEP = EPf - EPi

ΔEP = (0.050 kg · 9.81 m/s² · 3.0 m) - (0.050 kg · 9.81 m/s² · 70.0 m)

ΔEP = -32.9 J

c) When the pebbel is dropped, the potential energy will be:

EP = m · g · h

EP = 0.050 kg · 9.81 m/s² · 70.0 m = 34.3 J

d) When it reaches the net h = 3.0 m. Then:

EP = 0.050 kg · 9.81 m/s² · 3.0 m = 1.47 J

e) We have to add 30 J to the potential energy values calculated above:

The potential energy at 70.0 m will be: 34.3 J + 30 J = 64.3 J

The potential energy at 3.0 m will be: 1.47 J + 30 J = 31.47 J

6 0
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algol13
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