Kerala SSLC · Physics · Class 10
Work, Energy and Power: Important Questions with Answers
These are 10 important multiple-choice questions from the Kerala SSLC Physics chapter “Work, Energy and Power” (Kerala SCERT syllabus). Each one shows the correct answer and a short explanation of why it is right. Try answering before you read the answer. ExamSummary has 10 practice questions on this chapter in total.
Q1.A satellite revolves around the Earth in a circular orbit. What is the work done by the gravitational force acting on the satellite?
- A)Zero
- B)Positive
- C)Negative
- D)Infinite
Answer: A) Zero
The gravitational force acts towards the center of the Earth, while the displacement is tangential to the orbit. Since the force is perpendicular to the direction of motion (90 degrees), the work done is zero.
Q2.A person carries a heavy load on their head and walks horizontally on a flat road. The work done by the person against gravity is:
- A)Maximum
- B)Minimum
- C)Zero
- D)Equal to weight × distance
Answer: C) Zero
The force exerted by the person is upward to balance gravity, but the displacement is horizontal. Since the force and displacement are perpendicular, the work done against gravity is zero.
Q3.Which of the following represents the commercial unit of electrical energy?
- A)Joule
- B)Watt
- C)Kilowatt-hour
- D)Horsepower
Answer: C) Kilowatt-hour
While the SI unit of energy is the Joule, the commercial unit used for billing electricity consumption is the Kilowatt-hour (kWh).
Q4.According to the law of conservation of energy, energy can be:
- A)Created but not destroyed
- B)Destroyed but not created
- C)Transformed from one form to another
- D)Lost completely during transformations
Answer: C) Transformed from one form to another
The law states that energy cannot be created or destroyed; it can only be transformed from one form to another, such as potential energy converting to kinetic energy.
Q5.When a ball is thrown vertically upwards, at its highest point, its kinetic energy is:
- A)Maximum
- B)Minimum (zero)
- C)Equal to potential energy
- D)Infinite
Answer: B) Minimum (zero)
At the highest point of the trajectory, the instantaneous velocity of the ball is zero. Since kinetic energy depends on velocity, it becomes minimum (zero) at this point.
Q6.Frictional force always does:
- A)Positive work
- B)Negative work
- C)Zero work
- D)Variable work
Answer: B) Negative work
Frictional force always acts in the opposite direction to the displacement of the object. Since the angle between force and displacement is 180 degrees, the work done is negative.
Q7.If the velocity of a moving car is doubled, its kinetic energy becomes:
- A)Twice the original value
- B)Four times the original value
- C)Half the original value
- D)Unchanged
Answer: B) Four times the original value
Kinetic energy is directly proportional to the square of the velocity (KE = (1)/(2)mv²). Therefore, doubling the velocity results in the kinetic energy increasing by a factor of four.
Q8.Two students, A and B, climb the same flight of stairs. Student A takes 20 seconds and Student B takes 10 seconds. Who exerts more power?
- A)Student A
- B)Student B
- C)Both exert equal power
- D)Cannot be determined
Answer: B) Student B
Power is defined as work done per unit time (P = W/t). Both students do the same work against gravity, but Student B takes less time, resulting in higher power output.
Q9.Calculate the work done in lifting a 10 kg mass to a height of 5 meters (take g = 10 m/s²).
- A)50 J
- B)500 J
- C)100 J
- D)1000 J
Answer: B) 500 J
Work done against gravity is calculated as W = mgh. Substituting the values: 10 × 10 × 5 = 500 Joules.
Q10.One kilowatt-hour (kWh) is equivalent to how many Joules?
- A)3.6 × 10⁶ J
- B)3.6 × 10³ J
- C)1000 J
- D)3600 J
Answer: A) 3.6 × 10⁶ J
1 kWh equals 1000 Watts multiplied by 3600 seconds. This calculation yields 3,600,000 Joules or 3.6 × 10⁶ Joules.