Push along, and count the joules

Science · Energy · ages 15-16

Name ______________________ Date ____________

A force of 50 N pushes a box 4 m along the force. How much work is done in J?
Answer: ______________
What is work done?
- Force times distance along the force
- Force divided by distance
- Mass times speed
Carrying a bag along a flat corridor does work against the lifting force.
Circle one: True False
Which row gives the correct units?
- Watts for work, joules for power
- Joules for work, watts for power
- Newtons for work, joules for power
A motor does 1200 J of work in 5 s. What is its power in W?
Answer: ______________
You push a wall that never moves. How much work do you do?
- Some, effort counts
- None, nothing moved
- Double, time counts
A student writes power = 1200 J times 5 s. What is wrong?
- Work should be in watts
- Seconds should be minutes
- Time should divide, not multiply
A crane does 3000 J of work in 20 s. What is its power in W?
Answer: ______________

Answer key

For grown-ups. Fold this page away before handing over the rest.

200 · 50 times 4 = 200 J.
Force times distance along the force · Work = force times distance moved along that force, in joules.
False · The motion runs sideways to the upward pull, so no work counts against it.
Joules for work, watts for power · Work is joules, power is watts, time is seconds.
240 · Power = work divided by time: 1200 divided by 5 = 240 W.
None, nothing moved · No distance along the force means zero work, however tired you feel.
Time should divide, not multiply · Power is work divided by time. Units agree: joules over seconds give watts.
150 · 3000 divided by 20 = 150 W.