 µ IB | Energy + Power

10 quick questions

10 minutes maximum! (can you do it in 5?)

For all these questions you may take g = 10 ms-2.

1-3. A bowling ball of mass 6 kg rolls down a frictionless slope as shown here: 1. What is the gravitational potential energy of the ball at the top of the slope?

• A. 18 J
• B. 300 J
• C. 180 J
• D. 30 J

2. What is the kinetic energy of the ball at the bottom of the slope?

• A. 18 J
• B. 300 J
• C. 180 J
• D. 30 J

3. What is the impact velocity of the ball?

• A. √6 ms-1
• B. √60 ms-1
• C. √30 ms-1
• D. 60 ms-1

4. A 2 kg brick is held 1.5 m above the ground, and then thrown horizontally at 5 ms-1. Which of these gives the potential and kinetic energy of the brick just after being thrown?

 Kinetic Energy (J) Gravitational Potential Energy (J) A 5 3 B 25 3 C 25 30 D 50 30

5 & 6. An old light bulb is rated as having a 50 W input. It is left on for 5 minutes. 5. How much electrical energy is supplied to the bulb over this time?

• A. 15 kJ
• B. 3 kJ
• C. 250 J
• D. 600 J

6. What is the visible light output of the bulb if it is 20 % efficient?

• A. 10 W
• B. 5 W
• C. 25 W
• D. 250 W

7. A steel cable is used in a suspension bridge.

The cable is stretched by a distance x, storing E joules of elastic energy. What is the energy stored if the cable extension increases to 4x ?

• A. 2 E
• B. 4 E
• C. 8 E
• D. 16 E

8. A climbing rope is stretched, and the force and extension recorded. The rope produces a force-extension graph like this: The energy stored in the rope when it has an extension of x is:

• A. The area under the line
• B. The gradient of the line at x.
• C. F.x
• D. ½ F.x

9&10. A large concrete block is dragged 10 m along rough ground by a force of 800 N. The force acts at an angle as shown in the diagram. 9. The work done - in joules - in moving a distance of 10 m along the ground is:

• A. 800 cos θ
• B. 8000 cos θ
• C. 800 sin θ
• D. 8000 sin θ

10. If the block is pulled at a velocity of 2 ms-1, the power working against friction, measured in watts, is:

• A. 1600
• B. 16000
• C. 1600 cos θ
• D. 16000 cos θ