1. A duck with a mass of 4 kg experiences a drag force of 35 N while flying at 2

Question

1. A duck with a mass of 4 kg experiences a drag force of 35 N while flying at 20 m/s. How much work must the duck do in order to fly 100 km at constant speed? For reference 1 food calorie is about 4000 J 2. A spring in a toy gun has a spring constant of 10 N/m and can be compressed 4 cm. It is then used to shoot a 1 g ball out of the gun. Find the velocity of the ball as it leaves the gun. 3. A car with a mass of 800 kg moving 45 m/s slams on it's brakes and comes to a stop after traveling 45 m. What was the average force of friction acting on the car while it was braking? 4. A ball of clay with a mass of 100 g and a radius of 5 cm is thrown against a wall. It hits the wall with a purely horizontal velocity of 30 m/s. Find the average acceleration of the ball while it is hitting the wall 5. Your garage door is likely attached to a very large spring. This is done in order to make it easy to lift a large, heavy door with relatively little work. When the garage door is closed the spring is stretched and when its open the spring as at its unstretched length. Suppose you have a garage door with a mass of 100 kg that needs to be lifted 1.5 m when opening. You want the gravitational potential energy when the door is open to be equal to the spring potential energy when the door is closed If your spring stretches by the same distance your door moves, what spring constant does your spring need to have? 6. For the set-up in the previous problem if mechanical energy is conserved find the speed of the center-of-mass of the garage door as it goes from closed to open. Your answer should be speed as a function of center-of-mass height. Create a plot using a computer (Excel, Python, Wolfram Alpha, etc.) of the speed. 7. A 7 kW (about 10 horse-power) motor is used to lift a block that weighs 100 kg. Assuming the block is moving upwards at a constant velocity, what is that velocity?

Explanation / Answer

1)

W = Fdrag x S

W = 35 N x 100 x 10^3 m

W = 3500 KJ

2)

By the law of energy conservation

KEinitial = KE(final)

1/2kx^2 = 1/2mv^2

kx^2 = mv^2

v^2 = kx^2/m

v = x*sqrt(k/m)

v = 0.04*sqrt(10/0.001)

v = 0.04 x 100

v = 4 m/s

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.