<span>When a person lifts the block, the block has more potential energy. Therefore the person does positive work on the block.
work = m g h
work = (4.5 kg) (9.80 m/s^2) (1.2 m)
work = 52.92 joules
The person's work on the block is 52.92 joules
When the block is being raised, the force of gravity opposes the motion. Therefore the force of gravity does negative work on the block.
work = - (force) (h)
work = - m g h
work = -(4.5 kg) (9.80 m/s^2) (1.2 m)
work = -52.92 joules
The work done by the force of gravity on the block is -52.92 joules
Note that when the block is moved horizontally, the potential energy does not change. Therefore there is no work done on the block when it moves horizontally (we are assuming that the kinetic energy does not change).</span>
Answer:
- Distance between car and the deer when the car stopped = 20 m
- The time required for you to stop once you press the brakes = less than 5 s in order not to hit the deer.
Explanation:
Using the equations of motion,
In the 0.5 s reaction time, we need to first calculate how far he has travelled in that time.
a = 0 m/s² (Since the car is travelling at constant velocity)
x = ?
Initial velocity = u = 20 m/s
x = ut + at²/2
x = 20×0.5 + 0 = 10 m
From that moment,
a = - 10 m/s²
u = initial velocity at the start of the deceleration = 10 m/s
v = final velocity = 0 m/s
x = ?
v² = u² + 2ax
0² = 10² + 2(-10)(x)
20x = 100
x = 5 m
Total distance travelled from when the deer stepped onto the road = 10 + 5 = 15 m
Distance between car and the deer when the car stopped = 35 - 15 = 20 m
b) To determine the time required to stop once you step on the brakes
u = 10 m/s
t = ?
v = 0 m/s²
x = distance from when the brake was stepped on to the deer = 35 - 10 = 25 m
x = (u + v)t/2
25 = (10 + 0)t/2
10t = 50
t = 5 s
Meaning the time required to stop once you step on the brakes is less than 5s.
Answer:
John Dalton
Explanation:
Dalton's atomic theory was the foundation for a new understanding of chemical structures. He proposed that matter was constituted by indivisible and indestructible particles "atoms." He theorized that all atoms of a particular substance were equal, and the atoms of different substances had atoms of different sizes and masses.
He also proposed that all compounds of elements were combinations of elements but in a very precise ratio.
