Please help solve the problems. You throw a ball straight up. Compare the sign o

Question

Please help solve the problems.

You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down. A. Work is + on the way up and + on the way down. B. Work is + on the way up and - on the way down. C. Work is - on the way up and + on the way down. D. Work is - on the way up and - on the way down. A car accelerates from rest to a speed of 19.0 m/s in 6.00 seconds. If the car weighs 16,000 N, what average power must the motor produce to cause this acceleration? Use g= 10 m/s^2. A. 128 kW B. 15.0 kW C.49.1 kW D. 219 kW E. 481 kW

Explanation / Answer

(8) Correct option is (c)

Wg up =F.s = mgh cos(180) = -ve

Wg down =F.s = mgh cos(0) = +ve

(9) Correct option (c)

From work energy thorem W = Kf -Ki

W =(1/2)mv^2

m = w/g = 16000/9.8

W = [(1/2)(16000/9.8)(19*19)]

P =W/t = [(1/2)(16000/9.8)(19*19)]/ 6

P = 49.1 kW

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