Question

A 200 kg wagon climbs up a hill of slope 30-degrees in 1 minute at a speed of 36 km/h. How much power is delivered by the engine if the frictional force is 25% of the weight of the car? (Assume g = 10m/s^2)

(a) 25 kW

(b) 50 kW

(c) 100 kW

(d) 125 kW

I got this question in an international level competition.

Asked question is from Power in portion Work, Energy and Power of Physics – Class 11

Answer 1

The correct answer is (a) 25 kW

Easiest explanation: Weight of car = m x g

 = 200 x 10

 = 2,000 N

Frictional force = (25/100) x (2,000)

 = 500 N

Total force (F) = 2000 + 500

 = 2,500 N

Velocity (v) = 36 km/h

 = 36 x (1000/3600)

 = 10 m/s

P = F x v

 = 2500 x 10

 = 25 kW.