Question

A hairdryer transfers 36,000J in one minute, what is the power rating of the hairdryer?

Calculate the work done where 99W is used over 360s

Calculate the efficiency of a kettle which takes 100J and transfers it into 55J



Calculate work done when an object has an applied force of 5N and moves a distance of 4m

An electric fire needs 4 kW. It is switched on for 4 hours. If each kWh costs 2p, how much does it cost to run the fire?

Please help me quick I only have tomorrow left

Thank you ​

Answer 1

1. 600 watts

2. 35640 J

3. 55%

4. 20 J

5. The cost of running the fire is 8p.

Explanation:

1. Energy = 36 000 J , t = 1 minute = 60 seconds

Power =
`(energy)/(time)`

=
`(36000)/(60)`

= 600 watts

2. Power =
`(work done)/(time)`

⇒ work done = Power × time

= 99 × 360

= 35640 J

3. Efficiency = (Output / Input) × 100

=
`(55)/(100)` × 100

= 55%

4. Work done = Force × distance

= 5 × 4

= 20 J

5. Given that 1 KWh cost 2p, Power = 4 KW and time = 4 hours.

Power =
`(energy)/(time)`

Energy = Power × time

= 4 × 4

= 16 KWh

The cost of running the fire =
`(16)/(2)`

= 8p