SAMPLE LESSONS > O LEVEL WORK, ENERGY, POWER

# WORK DONE & ENERGY CONVERSION

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### ENEGRY CONVERSION CASE 1

### ENEGRY CONVERSION CASE 2

### WORK DONE

# WORKED EXAMPLES

#### EASY

##### A coconut of mass 600 g falls from a height of 30 m. Ignoring air resistance, what is the speed of the coconut before it hits the ground?

##### Answer

#### MEDIUM 1

##### A ball of mass 40.0 g is fired from a source horizontally at a speed of 125 m/s. The ball collides with a stationary object X of mass 500 g and is stuck with it. Both the ball and object X now move together at a horizontal speed of 10 m/s immediately after the collision. They both swing upwards to a vertical height of *h* from the original position before coming to a stop.

##### a) What is the kinetic energy o the ball before it hits object X?

##### b) What is the kinetic energy of the ball and object X after both collide and are stuck together?

##### c) Using the kinetic energy in (b) and the fact that air resistance is negligible, calculate the height *h*.

##### Answer

#### MEDIUM 2

##### A box of mass 0.5 kg is pushed along a slope from P to Q by a force *F* of 12 N as shown in the diagram below. Take *g* as 10 N/kg.

##### a) Calculate the work done by force *F* to move the box from P to Q.

##### b) Calculate the potential energy of the box at the top of the slope.

##### c) The work done by force *F* is not equal to the potential energy gained by the object at the top of the slope. Explain the discrepancy.

##### d) What is the work done against friction from P to Q?

##### Answer

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