# Work and Energy

1. Oct 20, 2005

### Weatherkid11

Please let me know if I am on the right track for these problems.
1) A weight lifter picks up a barbell and
1. lifts it chest high
2. holds it for 5 minutes
3. puts it down.
Rank the amounts of work W the weight lifter performs during this three operations. Label the quantities as W1, W2, and W3. Justify you ranking order. ---> I think that the most amount of work is when it is lifted chest high, since there is a force and displacement involved. After that, would me when he puts it down, becuase gravity helps, and there is a displacement. When he holds it up for five min there is no work becuase there is no displacement.
2)Estimate the amount of work the engine performed on a 1200 kg car as it accelerated at 1.2 m/s2 over a 150 meter distance. ----> Well since the equation for work is force times distance, it would be (1.2 m/s2)(1200kg)(150m) So the total work would be 216,000 J

2. Oct 20, 2005

### sanitykey

I think you are right for both questions, you've used the equations:

$$Wd=F \times d$$ and
$$F=m\times a$$

Where:

Wd is work done in Nm (Newton meters)
F is the force in N (Newtons)
d is the distance in m (meters)
m is the mass in kg (kilogrammes)

a is the acceleration in $$\frac{m}{s^2}$$ (meters per second squared)

I think you have interpreted and used these equations correctly.