Question

15. (a) A boy exerts a force of 4000 N to pull a cart at a constant speed of 30
m/s, calculate the power developed by the boy.
(b) The power of a motor is 40 kW. At what speed can it raise a load of
20,000 Newton?​

Answer 1

Answer:

b)

Explanation:

Correct option is

B

2ms−1

Power=work/time

Work=F×S

Power=F×S/t

Power=F×v where v is the velocity as it is rate of change of displacement

40000=20000×v

v=40000/20000=2m/s.

Answer 2

Question- 1 :-

$\dag\:Given :-$

• Force exerted by body 4000N
• Constant speed 30 m/s

i.e

• F = 4,000N
• v = 30 m/s

$\dag\: To\: find:-$

• Power

$\dag\: Solution$

As we have formula to find the power that is

P = F × V

• F = force
• v = velocity

Substituting the values

P = 4,000 × 30

P = 1,20,000 W

So, Power developed by the body is 1,20,000 watts

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Question- 2

$\dag\:Given :-$

• Power of body is 40 kW
• Force exerted is 20,000 N

$\dag\:To\: find :-$

• Speed

$\dag\:Solution :-$

Firstly lets convert the kW to watts

1kW = 1000 watt

So,

40kW = 40×1000

= 40,000watt

Power = 40,000 watts

Force = 20,000 N

Applying the same formula again

P = F × V

40,000 = 20,000 × V

4 = 2v

v = 4/2

v = 2 m/s

So, speed of the body is 2m/s

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$\dag\:Know\: more :-$

Power is defined as work done per unit time is called power that is

P = w /t

Units of power is watt

Other unit :- horse power .

1 horse power = 746 watt

Dimensional formula:- [ML²T^-3]

Power is a scalar quantity

Other formula to find power is

P = F× V