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

1. 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: $E = mc^{2}$)

2. A crane lifts a load of 6000 N through a vertical distance of 15 m in 30 s.

What is the average useful power during this operation?

3. A teacher carries a stack of books weighing a total of 30N through 2m. What is the work done by the teacher?

4. An object that has a mass of 15 kg on the Earth is taken to the Moon.

The gravitational field strength on the Earth is $10 \text{ N kg}^{-1}$ and on the Moon is $1.6 \text{N kg}^{-1}$.

What are the mass and weight of the object on the Moon?

	Mass (kg)	Weight (N)
A	15	24
B	15	150
C	24	15
D	150	24

5. The mass of a paper-clip is 0.50 g and the density of its material is $8.0 \text{ g cm}^{-3}$. The total volume of a number of paper-clips is $20 \text{ cm}^{3}$.

How many paper-clips are there?

6. A mass hangs on a string fixed at point P. It starts from position 1 and swings to the furthest position on the opposite side, position 2. It then oscillates several times with decreasing amplitude before ending at position 3.

Where does the ball have the most kinetic energy?

7. Ten identical steel balls, each of mass 27 g, are immersed in a measuring cylinder containing 20 $cm^{3}$ of water.

The reading of the water level rises to 50 $cm^{3}$.

What is the density of the steel?

8. 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?

9. When a spring is compressed, what form of energy does it possess?

10. Which energy changes take place when a pedalling cyclist uses a generator (dynamo) to light his bicycle lamp?