Work and Energy Transfers

When a ball is thrown vertically upwards, what happens to its kinetic energy as it reaches the highest point of its trajectory?

• Remains constant

• Becomes zero

• Decreases

• Increases

Answer explanation

As the ball reaches the highest point of its trajectory, its kinetic energy becomes zero due to the change in direction of motion.

What unit is used to measure work done?

• Watt

• Joule

• Newton

• Meter

Answer explanation

The unit used to measure work done is the Joule. It is defined as the work done by a force of one newton acting over a distance of one meter.

If a force of 5000 Newtons is applied to a car's brakes and it takes 20 meters to stop, how much work is done?

• 100,000 Joules

• 50,000 Joules

• 200,000 Joules

• 10,000 Joules

Answer explanation

Work done = force x distance = 5000 N x 20 m = 100,000 Joules

If a force of 10 Newtons moves an object by 5 meters, how much work is done?

• 15 Joules

• 50 Joules

• 5 Joules

• 100 Joules

Answer explanation

Work done = force × distance = 10 N × 5 m = 50 Joules. Therefore, the correct answer is 50 Joules.

What happens to the temperature of the brakes when a car stops?

• Decreases

• Stays the same

• Depends on the force applied

• Increases

Answer explanation

When a car stops, the temperature of the brakes increases due to the friction generated as the brakes are applied to stop the car.

What is work done?

• The distance an object travels

• The force applied to an object

• The energy transferred when a force moves an object

• The temperature increase of an object

Answer explanation

Work done is the energy transferred when a force moves an object.

How is work done calculated?

• Distance divided by time

• Force multiplied by time

• Force divided by distance

• Force multiplied by distance

Answer explanation

Work done is calculated by multiplying the force applied by the distance over which the force is applied.

What is the relationship between force, distance, and work done?

• No relationship

• Depends on the object

• Direct

• Inverse

Answer explanation

The relationship between force, distance, and work done is direct. As force or distance increases, the work done also increases.

If a person with a mass of 70kg Newtons climbs 10 meters, how much work is done?

• 7000 Joules

• 700 Joules

• 70 Joules

• 7 Joules

Answer explanation

The work done is calculated using the formula: work = force × distance. Here, the force is the person's weight (70kg × 9.8m/s^2) and the distance is 10 meters. So, work = 70kg × 9.8m/s^2 × 10m = 7000 Joules.

What type of energy transfer occurs in a hairdryer?

• Both kinetic and thermal energy

• Electrical energy

• Thermal energy only

• Kinetic energy only

Answer explanation

A hairdryer transfers both kinetic energy (from the moving air) and thermal energy (from the heat produced) to dry and style hair.