# Physics -Work probelm

1. Oct 28, 2004

### kmotoao

i need help on this problem. thx

A 47.0 kg projectile is launched with an initial speed of 72.0 m/s and an angle of 39.8° above the horizontal. The projectile lands on a hillside 7.15 s later. Neglect air friction. (a) What is the projectile’s kinetic energy at the highest point of its trajectory? (b) What is the height of the impact point? (c) What is its total energy just before it hits the hillside?

2. Oct 28, 2004

### Galileo

For a) Use an energy approach (obiousvly).

$$K=\frac{1}{2}mv_x^2+\frac{1}{2}mv_y^2$$
and $E=K+V$.
You know E from the initial conditions.
At the highest point the velocity in the y-direction is zero.

b) I'd look at the y-component only and write the height as function of time. Then find the height of the impact point.

c) Use conservation of energy again.