Solutions to the Quiz on Enertia, Kinetic Energy, and Coulomb's Law

Question 1: An object that is negatively charged:
Answer: has gained electrons.

Question 2: Describe the motion of a driver not wearing his/her seat-belt when the car suddenly stops.

Answer: The car will stop and the person will keep moving forward because of inertia.

Question 3: If visitors travel all the way to the moon. Describe the change.

Answer: weight of the visitors.
Explanation: Mass does not change but since the gravity changes so would the weight.

Question 4: The diagram below shows a moving, 5-kg cart at the foot of a hill 10.0 meters high.
Motion
For the cart to reach the top of the hill, what is the minimum kinetic energy of the cart in the position shown?
Assume that energy loss due to friction is negligable

Answer: 490 J
Explanation: Kinetic enregy = F × d = 5 kg × 9.8 × 10 m = 490 J

Question 5: See the figure below and determine the kinetic energy of the rock when it reaches the ground.
kinetic-energy-rock
Answer: 44,100 J
Explanation: Kinetic enregy = F × d = 50 kg × 9.8 × 90 m = 44,100 J

Question 6: A ball moving at 80 m/s has a momentum of 20 kg·m/s.
Calculate the mass of the ball.

Answer: 0.25 kg.
Explanation: momentum = mass × speed, and so mass = momentum / speed = 20 / 80 = 0.25 kg.

Question 7: Consider a truck has a linear momentum of 30,000 kg⋅m/s, and it is moving at 10 m/s.
Calculate is its mass.

Answer: 3,000 kg.
Explanation: momentum = mass × speed, and so mass = momentum / speed = 30,000 / 10 = 3,000 kg.

Question 8: A squirrel leaps from its resting position at the near tree onto a golf course.
If the squirrel has a mass of 0.8 kg and the acceleration of the leap is 5 m/s2,
Find the force the squirrel exerts when leaping?

Answer: 4.0 m/s2
Explanation: F m × a = 0.5 × 5 = 4 m/s2

Question 9: How do you compare magnitude of the electrical charge carried by an electron with he magnitude of the charge on an electron proton?

Answer: Exactly same.
Question 10: The magnitude of the electric force between two protons is 5× 10− 26 N.
Find the distance between the two protons.

Answer: 0.071 m
Explanation: Coulomb's formula F = k(q1q2)/ r2 where r is the distance and k = 8.99 × 109, and q1 = q2 = 1.6× 10− 19 C
Using the above Coulomb's formula, 5× 10− 26 N = 8.99 × 109 ((1.6× 10− 19) × (1.6× 10− 19)) / (r2)
5× 10− 26 = (25.65 × 10− 29) / (r2), and we obtain r2 = 0.00513 m, which means r = 0.071 m.

Question 11: A sister pushes her 10-kg little brother, who is sitting on a swing.
Assumne the sister exerts a 8-newton force on the child for 0.40 second, calculate the magnitude of the impulse imparted to the child by his sister.

Answer: 0.4 N
Explanation: Using the Newton's second law F = m×a = m × Δv /t and if both sides are multiplied by t we obtain F ×t = m × Δv which represent the impulse in Physics.
Hence the impulse imparted to child = 8 N × 0.4 s = 0.4 N•s

Question 12: Which of the following is an energy unit?

Answer: Joule


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Date of last modification: Summer , 2019