# Work

## Problems

### practice

- Write something.
- Write something else.
- Write something different.
- Write something completely different.

### numerical

- An 11.3 g bullet leaves the muzzle of a 61 cm rifle with a horizontal velocity of 922 m/s. Determine…
- the acceleration of the bullet in the rifle
- the force of the propellant on the bullet in the rifle
- the work done on the bullet while it is in the barrel

- the horizontal acceleration of the bullet as it flies through the air
- the force of aerodynamic drag on the bullet
- the work done by aerodynamic drag on the bullet

- A group of students are performing an experiment to measure the coefficient of friction between a wood block and a wood plank. One of the students pulls on the block with a force that increases from 0.000 N to 4.135 N in 0.5 seconds. The students are not able to overcome the static friction force.
- How far did the block move during this part of the experiment?
- How much work was done on the block during this part of the experiment?

- How far did the block move during this part of the experiment?
- How much work was done on the block during this part of the experiment?

- coefficient of static friction for wood on wood
- coefficient of kinetic friction for wood on wood

- A model rocket has mass of 1.5 kg. The engine exerts an effective upward thrust of 120 N for 3.2 seconds. (Assume a negligible amount of air resistance and no change in mass while the rocket is ascending.)
- Draw a free body diagram showing all the forces acting on the model rocket.

- the weight of the rocket
- the net force on the rocket while the engine was running
- the acceleration of the rocket while the engine was running
- the distance traveled by the rocket while the engine was running
- the speed of the rocket when the engine stopped
- the work done by the engine on the rocket

- Draw a free body diagram showing all the forces acting on the model rocket after the engine shut down.
- What is the acceleration of the rocket after the engine shut down?
- What maximum height above the ground did the rocket reach?
- How much work did gravity do on the rocket from launch until it reached its maximum height?

- If your answers to part g. and part k. are not equal (to within 2 or 3 significant digits), you've made a mistake somewhere. If they are equal, you've probably done it correctly (probably).

- A 1125 kg car is driven up a 9° ramp at a constant speed of 2.5 m/s for 20 s. Assuming negligible friction, determine…
- the weight of the car
- the force of the tires pushing the car up the ramp
- the distance the car traveled up the ramp
- the increase in height of the car
- the work done by the engine pushing the car up the ramp

- A force of 90 N is applied by a homeowner to a 35 kg lawnmower along a handle that makes a 30° angle with the vertical. The lawnmover is moving forward across level ground at a constant velocity.
- Draw a free body diagram showing all the forces acting on the lawnmower. Do not resolve any of the forces into components. Do indicate their directions, however.

- the gravitational force of the Earth
- the normal force of the ground
- the force applied by the homeowner
- the force of friction from the ground

- the gravitational force of the Earth
- the normal force of the ground
- the force applied by the homeowner
- the force of friction from the ground

- The graph below shows applied force vs. displacement for an ultralight airplane.
- What does the area under this curve represent?
- Calculate its cumulative value at 200 m intervals. Compile your results in a table like the one below.

interval ending at 0.0 km 0.2 km 0.4 km 0.6 km 0.8 km 1.0 km interval area cumulative area - Sketch a graph of this quantity with respect to displacement.