A or C is the right answer.
Answer:
you are using your shoulder muscle. The reason you are using this muscle is when you put your arm strait up there is no reason to use a bicep or tricep muscle.
Explanation:
Force required = F = ?
mass of the car = m = 1200 kg
initial velocity of the car = Vi = 10 m/sec
final velocity of the car = 0
time required to stop the car = t = 20 sec
Using Newton`s 2nd law of motion;
F = ma ………………………(1)
as a = Vf - Vi / t , put this value in equation (1)
F = m ( Vf - Vi /t ) ………………(2)
F = 1200 ( 0 - 10 /20) = - 600 N
here Negative sign shows that external force is acting in opposite direction of the motion to bring it to rest.
we can also calculate this force by using the relation
Rate of change of momentum = net force acting on the object …………(3)
m Vf - m Vi / t = net force acting on the object
m (Vf - Vi / t) = F
1200 ( 0 - 10 /20) = - 600 N = F
so, net force acting on the object =F = - 600 N
Answer: B
Explanation: when coal lights it gives off heat energy
