Answer
given,
mass of the ball = 3 kg
swing in vertical circle with radius = 2 m
work done by the gravity = ?
work done by the tension = ?
Work done by the gravity = - m g Δh
Δ h = 2 + 2 = 4 m
Work done by the gravity =
= -117.6 J
work done by gravity is equal to -117.6 J
Work done by tension will be equal to zero.
Zero because tension is always perpendicular to velocity
work done by tension is equal to 0 J
After 6 seconds, the car will surpass the cyclist.
<h3><u>Explanation:</u></h3>
The speed of the cyclist = 6 m/s.
Let after time t sec, the car will overtake the cyclist.
So, distance covered by the cyclist in t sec = 6t m
Initial velocity of the car is 0 m/s, because the car is just starting.
Acceleration of the car =
.
Final velocity of the car =6 m/s.
So to cover the distance 6t, the time required by the car = 

t =6 sec
So, after 6 seconds, the car will surpass the cycle.
The heat required to convert the unknown substance X from one phase to another is 1600 J times the specific heat of that substance.
Explanation:
The heat energy required to convert a substance or to heat up or increase the temperature of a substance can be obtained from the specific heat formula.
As per this formula, the heat energy applied should be equal to the product of mass of the substance with temperature gradient and also with specific heat of the substance. Basically, the heat provided to increase or convert a substance should be more than the specific heat of the substance.

Since, here the mass of the substance X is given as m = 20g and the temperature change is given from -10°C to 70°C.
Then ΔT = (70-(-10))=70+10=80°C.
As the substance is unknown, the specific heat of that substance can also not be determined. Hence keep it as C.

Q = 1600C J
Thus, the heat required to convert the unknown substance X from one phase to another is 1600 J times the specific heat of that substance.
Answer:
D:
Explanation:
Conduction because the heat energy is transferring directly from the separate metals convection involves "currents" like in a liquid or a gas. When you turn on the stove with a pot of water on the burner the water at the bottom of the pot gets heated first almost immediately this water rises and cooler water falls. Basically the water is "stirring" or shifting, exchanging the heat energy this is why water heats so evenly.