Practice MCQs For Mass, Weight and Density, Work, Energy and Power

1. Ali uses a 3 kW heater and a 100 W lamp together for a certain period of time. During this time, the lamp uses 0.5 kWh of energy. How much energy is used by the heater during this same period?

2. A man weighs 600 N. He runs up stars of total height 4 metres in 3 seconds. How much power is exerted by the man?

3. A rock on the Moon has a mass of 0.5 kg. It is brought to the Earth where the gravitational field is stronger. On the Earth, the rock will have _________ .

4. A box X full of large granite rocks is weighed. An identical box Y full of small granite chippings is then weighed.

Which box weighs more and why?

5. The acceleration of free fall on the Moon is $\frac{1}{6}$ of the acceleration of free fall on the Earth. Two pieces of rock, A and B, have the same volume. A is placed on the Moon and B is placed on Earth. If both of them have the same weight, what is the ratio of A's density to B's density?

6. When a nucleus of Uranium-235 absorbs a neutron, nuclear fission occurs. In a typical reaction, the total mass decreases by $3 \times 10^{-28}$ kg.

Given that the speed of light c is $3 \times 10^{8}$ m/s, approximately how much energy is released?

 

Hint: (Use Einstein's mass equivalence equation: $E = mc^{2}$)

7. What can be used as the unit of energy?

8. Four objects (A, B, C, D) are situated in places with different gravitational field strengths.

Which object has the greatest weight?

	Mass (kg)	Gravitational Field Strength ($\text{N kg}^{-1}$)
A	3.0	10.4
B	3.5	9.5
C	4.0	10.2
D	4.5	9.0

9. Which statement is correct about the position of the centre of gravity of a uniform solid?

The centre of gravity of a uniform solid

10. Consider a stationary box at height x. The block is lifted by a student such that it comes to a rest at higher height y.

Consider the following discussion between two students:

Student 1: I exert an upward force on the box, which moves upward, so I do positive work on the box. The Earth exerts a downward force, so it does negative work on the box. The box begins and ends at rest, so its kinetic energy hasn't changed. That means that the net work on the box is zero, so the work on the box by my hand and the work on the box by the Earth must have the same absolute value.

Student 2: But the box has moved upward, so its potential energy has increased. That means that the net work on the block must be positive, so the work on the box by your hand must be greater than the work on the box by the Earth.

What can you say about the reasoning given by the two students?