discussion | summary | practice | problems |

## 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 bullet strikes a target 457 m away with a horizontal velocity of 650 m/s. Determine…

- 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?

After the block starts moving, the students apply a new force of 2.164 N and the block moves with a constant speed of 0.0055 m/s for an additional 5.5 s.

- 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?

The students used a 1 kg wooden block to perform this experiment. Determine the…

- 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.

Determine…

- 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

After the engine shuts down, the rocket is still moving upward.

- 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.

Determine the magnitude of each of the following forces on the lawnmower.

- 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

Determine the work done by each of the following forces on the lawnmower if it is pushed forward 100 m…

- 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.