The plaintiff, voluntarily and without any obligation to do so, placed himself upon the hood of a truck in order to weight down its bumper so that the track might push an automobile until its motor started. He was fully aware that the hood was smooth and there was nothing on it to which he could hold. He also knew, or should have reasonably anticipated, that there might be jerks or bumps likely to cause him to lose his balance or to throw him from the truck while it was in motion. The injuries he sustained were the result of the risks to which he deliberately exposed himself. In thus placing himself in a position of obvious -peril, the plaintiff was guilty of contributory negligence which barred his right to recover as a matter of law and necessitated the nonsuit. Bogen v Bogen, 220 N.C. 648, 18 S.E. 2d 162; Barnes v. Horney, 247 N.C. 495, 101 S.E. 2d 315.
A seventeen-year old plaintiff is presumed to have sufficient capacity to understand and avoid a clear danger, and he is chargeable with contributory negligence .as a matter of law if he fails to do so. Tallent v. Talbert, 249 N.C. 149, 105 S.E. 2d 426; Van Dyke v. Atlantic Greyhound Corp., 218 N.C. 283, 10 S.E. 2d 727; Rimmer v. R. R., 208 N. C. 198, 179 S.E. 753; Baker v. R. R., 150 N.C. 562, 64 S.E. 506; 38 Am. Jur., Negligence, § 205, p. 891; 3 Strong, N. C. Index, Negligence, § 16. There is no evidence in the record which would overcome this presumption.
Plaintiff now contends, however, that after he had placed himself in a position of peril, he was thrown from the truck only because Carter negligently increased its speed to forty-five miles per hour. This contention is not supported by either allegation or proof. We take judicial notice that a truck traveling forty-five miles per hour cannot be stopped in thirty-three feet as plaintiff’s evidence indicates *308this truck was. Evidence which is inherently impossible will not take a case to the jury. Jones v. Schaffer, 252 N.C. 368, 114 S.E. 2d 105.
The question oí Carter’s agency and authority, debated in the briefs, is rendered moot by the plaintiff’s contributory negligence.
The judgment of the court below is