Question

(A) A heating appliance produces \(7200000\ \text{J}\) heat in 2 hours.

• [(a)] What is the energy change in a heating appliance?
• [(b)] Calculate the power of the appliance.

OR (B) An electric grinder with a power of \(400\ \text{W}\) is working.

• [(a)] What is the energy change in this equipment?
• [(b)] Calculate the work done by this grinder in 1 minute.

Hint:

Power \(P = \frac{E}{t}\), \quad Work \(W = Pt\)

Answer 1

(A) Heating appliance
(a) Energy change
Concept:
A heating appliance converts: \[ \text{Electrical energy} \rightarrow \text{Heat energy} \] Conclusion (a): \[ \text{Electrical energy is converted into heat energy} \] (b) Power calculation
Step 1: Given data}
\[ E = 7200000\ \text{J}, \quad t = 2\ \text{hours} = 2 \times 3600 = 7200\ \text{s} \] Step 2: Formula}
\[ P = \frac{E}{t} \] Step 3: Calculation}
\[ P = \frac{7200000}{7200} = 1000\ \text{W} \] Conclusion (b): \[ \text{Power} = 1000\ \text{W} \] (B) Electric grinder
(a) Energy change
Concept:
An electric grinder converts: \[ \text{Electrical energy} \rightarrow \text{Mechanical energy} \] Conclusion (a): \[ \text{Electrical energy is converted into mechanical energy} \] (b) Work done
Step 1: Given data}
\[ P = 400\ \text{W}, \quad t = 1\ \text{minute} = 60\ \text{s} \] Step 2: Formula}
\[ W = P \times t \] Step 3: Calculation}
\[ W = 400 \times 60 = 24000\ \text{J} \] Conclusion (b): \[ \text{Work done} = 24000\ \text{J} \]