Work Energy Power Efficiency

A motorist travelling at 10 ms^–1 can bring his car to rest in a braking distance of 10m. In what distance could he bring the car to rest from a speed of 30 m s^–1 using the same braking force?

• 17m

• 30m

• 52m

• 90 m

Tags

NGSS.HS-PS2-1

A stone of weight 4.0 N in the Earth’s gravitational field is moved from P to Q and then to R along the path shown.

How much potential energy does the stone gain?

• 120 J

• 200 J

• 280 J

• 1200 J

Tags

NGSS.MS-PS2-4

NGSS.MS-PS3-2

The total energy input E_in in a process is partly transferred to useful energy output U, and partly to energy that is wasted W. What is the efficiency of the process?

• 
• 
• 
• 

Tags

NGSS.HS-PS3-1

An object is thrown into the air. Which graph shows how the potential energy E_p of the object varies with height h above the ground?

• 
• 
• 
• 

A pendulum bob oscillates between P and R.

Assuming the gravitational potential energy lost in moving from P to Q is converted into kinetic energy, what is the speed of the bob at Q?

• 
• 
• 
• 

Which operation involves the greatest mean power?

• a car moving against a resistive force of 0.4kN at a constant speed of 20ms^–1

• B a crane lifting a weight of 3kN at a speed of 2ms^–1

• C a crane lifting a weight of 5kN at a speed of 1ms^–1

• D a weight being pulled across a horizontal surface at a speed of 6 m ^s–1 against a frictional force of 1.5kN

A system with an efficiency of 74% wastes 230W of power.

What is the useful output power of the system?

• 170W

• 310W

• 650W

• 880W

A projectile of mass 0.25 kg is at a height of 30m above horizontal ground and travelling at a speed of 15 m s^–1. A short time later, it is at a height of 35 m above the horizontal ground and travelling at a speed of 5.0 m s^–1. How much work is done against air resistance during this time?

• 0 J

• 13 J

• 25 J

• 37 J

Tags

NGSS.HS-PS3-1

A student is asked to determine the output of a motor as it lifts an object.

He measures the height through which the object is raised, the time taken and the weight of the object. To find the power he must calculate

• 
• 
• 
• 

A freely falling object on Earth has a speed of 5.0 m s^–1. After falling a further 20 m its speed is

• 15 m s^–1

• 20 m s^–1

• 25 m s^–1

• 45 m s^–1

Tags

NGSS.HS-PS2-1