Work and Energy quiz

The SI unit of work is:

The kinetic energy of an object of mass m moving with velocity v is:

1 kWh is equal to:

If the velocity of an object is doubled, its kinetic energy becomes:

Work done by a force is zero when the angle between force and displacement is:

The energy possessed by a stretched rubber band is:

Power is defined as:

The work done by friction on a moving object is usually:

An object of mass 2 kg is at a height of 5 m. Its potential energy is (g = 10 m/s^2):

In a freely falling body, the sum of kinetic and potential energy:

Give two examples of conversion of energy from one form to another. (2 marks)

Why is no work done by the gravitational force of the Sun on the Earth in its nearly circular orbit? (2 marks)

What is the work done by a person holding a 20 kg bag stationary for 10 minutes? Why does he feel tired? (2 marks)

What is average power? (2 marks)

Name the energy possessed by a flowing river and by water stored in a dam. (2 marks)

What is the relation between 1 kW and 1 W, and between 1 kWh and 1 J? (2 marks)

Why does an object thrown upwards slow down as it rises? Explain in terms of energy. (2 marks)

What happens to the potential energy of an object when its height is doubled? (2 marks)

Give an example where potential energy changes into kinetic energy. (2 marks)

Can an object have energy without having momentum? Give an example. (2 marks)

A pair of bullocks exerts a force of 140 N on a plough. The field is 15 m long. How much work is done in ploughing the length of the field? (3 marks)

A ball of mass 0.5 kg is moving at 20 m/s. Find its kinetic energy. How much work is needed to stop it? (3 marks)

A 60 kg man runs up a flight of 45 steps, each 20 cm high, in 9 s. Find his power. (Take g = 10 m/s^2.) (3 marks)

An electric bulb of 60 W is used for 6 hours a day. Find the energy consumed in a day in joules and in kWh. (3 marks)

The velocity of a 1000 kg car increases from 5 m/s to 10 m/s. Find the work done on the car. (3 marks)

Read the passage and answer the questions. A school installs a 2 kW water pump that lifts water to a tank on the roof. The pump runs for 3 hours a day. (i) Find the energy consumed by the pump in a day in kWh. (ii) Find the cost per month of 30 days at Rs 8 per unit. (iii) What form of energy does the water have in the tank? (5 marks)

Read the passage and answer the questions. A 4 kg ball is dropped from a height of 20 m. Take g = 10 m/s^2 and ignore air resistance. (i) Find its potential energy at the top. (ii) Find its kinetic energy just before it hits the ground. (iii) Find its speed just before it hits the ground. (5 marks)

Read the passage and answer the questions. A crane lifts a load of 1000 kg to a height of 15 m in 30 s. Another crane lifts the same load to the same height in 50 s. Take g = 10 m/s^2. (i) Find the work done by each crane. (ii) Find the power of each crane. (iii) Which crane is more powerful? (5 marks)

Read the passage and answer the questions. A boy pulls a toy car with a string with a force of 5 N and moves it by 4 m along the floor. Friction acts on the car with a force of 2 N. (i) Find the work done by the boy. (ii) Find the work done by friction. (iii) Find the net work done on the car. (5 marks)

Read the passage and answer the questions. A family's electricity meter showed a reading of 2450 units at the start of the month and 2690 units at the end. (i) How many units were consumed? (ii) Express this in joules. (iii) If the rate is Rs 6 per unit, find the bill. (5 marks)

Derive the formula for the kinetic energy of an object of mass m moving with velocity v. Draw a diagram and use the formula for a 1000 kg car moving at 20 m/s. (6 marks)

Draw a diagram and derive the formula for the potential energy of an object raised to a height h. Explain why the potential energy depends only on the height and not on the path taken. (6 marks)

Draw a diagram of a freely falling body and show with calculations that its mechanical energy is conserved, for a 2 kg body falling from 10 m (g = 10 m/s^2) at heights 10 m, 5 m and 0 m. (6 marks)

Draw a flowchart showing energy conversions in (i) a battery-operated toy car (ii) a solar cell (iii) a thermal power plant. Explain each. (6 marks)

Draw a diagram showing a force acting along, against and perpendicular to the direction of motion. Explain positive, negative and zero work with one example each. (6 marks)